Building Drainage E-Book

Kemi Adeyeye

• Herausgeber: Crowood
• Kategorie: Fachliteratur
• Sprache: Englisch

Veröffentlichungsjahr: 2019

Beschreibung

Good drainage contributes to the delivery of sustainable, innovative and resilient buildings, and is essential for our health and wellbeing. However, designers and architects can often leave drainage to be implemented by specialists in isolation of other design considerations, resulting in costly changes, rework and repairs, operational discomfort and poor user experiences that could have been avoided. Written for building designers and allied professionals, homeowners and managers as well as the general public, Building Drainage promotes an integrative and collaborative approach. Key principles and components of drainage design are presented in an accessible manner with many UK examples where the underlying information and knowledge can be applied internationally. coverage includes waste and foul water drainage systems and the benefits of integrated water management (IWM) approach, where 'waste' becomes a valuable resource; surface and rainwater drainage; water and energy efficiency through wastewater recycling and reuse, and heat recovery. After reading this book you will understand the mostly invisible, or unperceived, yet vital aspects of functional drainage design and their interaction with the architecture of the building as well as the local and global environments.

Leseprobe

BUILDING DRAINAGE

An Integrated Design Guide

Kemi Adeyeye and John Griggs

First published in 2019 by The Crowood Press Ltd Ramsbury, Marlborough Wiltshire SN8 2HR

www.crowood.com

This e-book first published in 2019

© Kemi Adeyeye and John Griggs 2019

All rights reserved. This e-book is copyright material and must not be copied, reproduced, transferred, distributed, leased, licensed or publicly performed or used in any way except as specifically permitted in writing by the publishers, as allowed under the terms and conditions under which it was purchased or as strictly permitted by applicable copyright law. Any unauthorised distribution or use of this text may be a direct infringement of the author’s and publisher’s rights, and those responsible may be liable in law accordingly.

British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library.

ISBN 978 1 78500 640 1

Contents

Preface }

Introduction }

Part 1: Outside the Building

Chapter 1 }Wastewater Drainage SystemsChapter 2 }Foul Water Drainage DesignChapter 3 }Surface Water DrainageChapter 4 }Rainwater Drainage

Part 2: Inside the Building

Chapter 5 }Internal Drainage DesignChapter 6 }Enhanced Drainage for Wastewater Heat Recovery and Water ReuseChapter 7 }Drainage at Water-Using Appliances and FittingsChapter 8 }Integration and Innovation

Index }

Preface

Drainage systems are a small, but vital, part of the water cycle. Until recently, drainage design and engineering practices have been implemented in isolation of natural processes and cycles but this trend is beginning to change. The Integrated Water Management approach considers all waters to be a resource with value. So, whereas previously, water from appliances, homes, factories and roads was considered to be ‘waste’ that simply needed to be got rid of, it is now considered better to look at each element of the discharged water and consider how it might be utilized or reduced, or even eliminated.

In developed countries, the inhabitants have become disconnected with any processes beyond their homes. Toilets are used and the ‘waste’ is flushed away, out of sight and out of mind. Water comes from a tap that produces an endless supply. If light is wanted, a switch is thrown and to adjust the temperature in a building a dial is turned or a button pressed. This disconnection from the natural forces and resources has made people naturally less sensitive to environmental issues. However, the research and increased media attention to environmental issues has created a change of mind in many users, planners and engineers so that the impact on our world is now becoming part of any design process, from a simple house extension to the development of a new city.

It is against this backdrop of a more integrated approach to the use, reuse and management of water that this book is written. The authors have drawn on traditional engineering as well as the latest research to provide a useful design guide to drainage systems fit for the twenty-first century.

How to Use this Book

•This book is not intended to be read cover to cover before you can understand any particular topic. However, it can be read in sequence, as the book is arranged in a logical sequence based upon the conventional drainage chain.

•As you read the various sections, you will build knowledge and insight about drainage systems of the past, present and future. You will see how changing expectations, awareness and lifestyles have impacted on drainage design.

•The photos that are included do not always show good examples of drainage installations, but real drainage. Often drainage systems are designed well, but suffer from poor installation and lack of maintenance; often the illustrations reflect this as a sobering warning that drainage systems are not ‘fit and forget’ items.

•Within the text you will find various references to legislation, standards and other guidance documents. Do not expect these to be consistent; many will offer very different ways of designing a wastewater system based upon very different priorities. You will need to decide what the requirements and priorities of your system need to be to find appropriate guidance that reflects your needs.

•Many of the standards that are referenced are based on well-established fluid dynamics principles. This is a good starting point, but most wastewater composition is complex and so rarely behaves as a ‘perfect fluid’. Although most drainage design equations will contain factors that aim to address the imperfection of wastewater and its pipework; these are often inadequate to deal with a system that ages and its operating conditions vary over time. Hence, most design principle are rules of thumb that need to be modified in the light to suit changing trends, as well as new and innovative products and fittings.

•The aim of the book is to make the reader think about any system, and not just follow a formula or a regulation.

•The issue of tolerances and accuracy is an important one that is touched upon in various places in the book. Some design parameters will be specified to tolerances of millimetres, others will have safety factors of two or three and some measurements will only be accurate within 200 per cent. So, designers are expected to understand and translate these guidelines to suit each individual project.

•Often you will find that different books, standards, regulations, etc. all use similar terms, but mean very different things. For example, a ‘drain’ in one country is defined as a ditch in another, and in another is a pipe of specific dimensions. Every effort has been made to ensure that this book is written in an accessible style so that the use of unexplained jargon is minimized and discussions are clear.

Fig. 0.1 The authors at work writing this book.

Introduction

Water is a naturally occurring element on Earth: of which 97 per cent is salt water and is mainly unusable without expensive, large-scale desalination plants. The remaining percentage consists of about 69 per cent ice and snow cover, 30 per cent groundwater and less than 1 per cent surface water held in lakes and rivers (UNEP 2002).

The built environment contributes to climate change, resource availability and the resilience of human beings and their associated social and economic activities. It also contributes significantly to our physical and mental health and well-being in numerous ways.

Therefore, the efficient and effective design, construction, operation, maintenance and deconstruction of buildings and the built environment is both necessary and essential. Hence, it is so important that architectural professionals understand and holistically address sustainable practices, alongside other important design considerations such as space, form, materials, aesthetics, etc.

Fig. 0.2 Water is central to our lives, for drinking, cooking, washing, heating, cooling as well as for aesthetics and recreation.

Modern sustainable buildings vary according to the level of resource use during construction and use in particular. Thus, the emerging characterizations and approaches to the production of buildings such as zero-carbon, low-carbon and carbon-negative buildings, as well as autonomous buildings and Huf Hauss.

The main vehicle for the delivery of sustainable buildings is through building services. Building services consists of heating, cooling, lighting, ventilation and plumbing systems. Each of these can contribute to the overall sustainable performance of a building.

Therefore, it is essential for architectural designers to consider the following during the design of any building:

•The size of the building and the different activity areas within and around it.

•The internal spaces, zoning and layout

•Occupancy and use of the building

•Thermal and acoustic insulation

•The heating systems

•The cooling systems

•Ventilation – how fresh air is moved around the building

•Hot and cold water provision in the building

•Electricity supply, generation and possibly storage

•Lighting systems for the building

•On-site renewable systems

•Building management systems or controls.

It is noteworthy that architectural design, i.e. site, form, spatial and aesthetics requirements, etc. all impact on the effectiveness of building services, and therefore the degree to which the building is sustainable and resource efficient.

This book is about water and wastewater drainage design in buildings. Water is used in the production, occupation and use of most buildings. Most building processes use water during on-site or off-site production, either through the production of dry walls in factories or through mixing mortar and concrete on site. Poor systems design can also result in supply issues, no or intermittent water coming out of the pipes, drips, water hammer and burst pipes due to excessive pressure, etc. In addition, site workers and building occupants use water directly for drinking, cooking, etc., and indirectly for cleaning, washing and waste disposal. The result of all of these activities is the production of waste or foul water. This by-product of water use needs to be appropriately ‘handled’ to avoid individual and public health and safety problems, e.g. foul odour, contamination and spread of diseases, etc., and to minimize the environmental impact such as the contamination of air, ground and water bodies.

The architectural and engineering design of the building needs to consider the type, positioning, access and management of drainage systems. In addition to delivering drainage systems that are both operationally effective and efficient, the decisions pertaining to water systems and drainage also impact on the degree to which the building is water efficient. This efficiency is increased by designing and specifying systems that help to reduce in-use water consumption, promote recycling, energy recovery and reduce the carbon/greenhouse, energy and environmental impacts associated with the collection, transportation, treatment and disposal of waste or foul water from buildings. Through good design, options for water conservation or reuse can be integrated into initial designs, product and fittings specification that would enable future reuse facilities to be incorporated simply at a later date. The routing of pipework can promote the waste of water (and energy) as users wait for hot water to arrive at the point of use. The pipe configuration can also enable or prohibit the immediate or future implementation of emerging innovations such as water recycling and reuse or heat recovery systems. The non-provision of storage, or its inadequate location or size within the building, basements or roof spaces during the design stages may also affect the ease of installation.

Early integration during the design stage is usually more beneficial, and cost effective, in building schemes or where facilities are shared between buildings, such as communal and district. Some building regulations now require integration with SuD (Sustainable Drainage) systems, so architects need to understand the local situation and regulations to maximize the sustainability of buildings or a scheme.

In addition to building regulations, there are many environmental assessment schemes that will include water use in their assessment procedures. International schemes include BREEAM, LEED, Green Star, DGNB and Estidama. Many of these national and local schemes incentivize innovative design approaches and technologies. It may be a clause within local planning or other regulations that requires a new, or refurbished, building to achieve a certain level of a specified environmental assessment scheme. Often, one of the simplest ways of achieving assessment ‘points’ is through water efficiency measures and the drainage system will need to be designed to work with volumes of water that may be far lower than in a comparable building without water efficient measures.

This book addresses some of the important water and drainage design considerations and provides key knowledge and insights to aid effective design decision making. It is primarily targeted at architects, architectural technologists or architectural engineers but it would also be of interest to anyone who is curious about the hidden (and sometimes noisy) aspects of their homes and site, the benefits of having a good water and drainage systems and insights into what is happening when things go wrong.

The Water Cycle and Balance

The simple water cycle diagram in Figure 3 that shows how water exists on the planet is familiar to most people. However, not everyone is fully aware of how human activity and interventions, in its various forms, affects the water cycle.

Fig. 0.3 The water cycle.

The amount of water used for human consumption in homes and places of work, in buildings, for agricultural, power generation, manufacturing and industrial processes, all impact on the built and natural environment. Too much can result in water ingress through roofs, flooding and landslides. Too little water in nature results in droughts, which affect water supply as well as drainage systems. Therefore, an understanding of the holistic water balance for all buildings, communities, rural or urban areas is paramount to make sure that we are resilient in this resource and avoid extreme human- or climate-induced cycles of surpluses and deficits.

In its simplest form, the water balance is a measure of water in and wastewater out, but it can rapidly become more complex when contributions from rainwater or greywater, infiltration, or even embedded water, are considered. The balance between water in and wastewater out should be more or less equal. However, there is increasing imbalance of water in nature due to modernization and urbanization, population growth, economic and industrial development. Technological innovation, however, makes it possible to address these deficits. For instance, it is now possible to recycle wastewater to drinking water standards. Thus we can become, in effect, water producers and not just consumers.

Water inConsumption/UseWastewater outRainfallGarden watering, vehicle washing, patio and path washing, ornamental ponds and water features

-Infiltration to local soil

-Evaporation

-Evapotranspiration via plants, or collection for reuse

Mains drinkable waterDrinking, culinary uses, showering, bathingBlackwater and greywater to sewers or local treatment or collection for reuseMains non-drinkable waterWC flushing, hand washingBlackwater and greywater to sewers or local treatment or collection for reuseRecycled greywaterWC flushingBlackwater to sewers or local treatment or collection for reuseCaptured rainwaterWC flushing, washing machinesBlackwater and greywater to sewers or local treatment or collection for reuse – as for rainfallCaptured condensateWC flushingBlackwater to sewers or local treatment or collection for reuse

Table 0.1 Detailed water balance.

Table 0.1 shows that the options for ‘wastewater out’ are no longer simply to drain. This shows why drainage has become so important in the whole water cycle for domestic uses and many industrial processes. The options for reuse or recycling are becoming more viable and less expensive. This opens up possibilities to many users. British, European, American and International Standards now make provisions for various forms of recycling and reuse in buildings. Therefore, although the planet’s overall use of water has increased, it is now possible, through good design and implementation of systems, to minimize the impact of the ever-expanding built environment on the amount and quality of available water in our localities.

The production and discharge of wastewater raises a number of environmental issues. Firstly, the safe collection and transportation of the wastewater (through the sewer system), then the treatment of the wastewater to enable reuse, or safe discharge back into the natural system. The latter entails the use of significant amounts of energy and the associated carbon and greenhouse gas emissions. In addition to the energy consumption associated with the treatment of water and wastewater, there are increasing concerns about the amount of nitrates and sulphates (e.g. from soaps using in washing), medications, oils and fat and other non-biodegradable waste that end up in the wastewater system. In 2017, a report by CIWEM highlighted the issue of fibre loss from clothes. It explained that when clothes are washed they lose fibres, which are washed away into the drains and eventually make their way to the oceans, where they are consumed by fish and enter the food chain. This is particularly a problem with the volume of synthetic materials as well as plastics in the seas and the food chain. A quick examination of the filter on a tumble dryer will indicate how much fibre is lost during a typical wash. In fact, about 700,000 fibres can be released from a typical 6kg wash load. Figure 0.6 from the report shows how wastewater contributes to the problem.

Fig. 0.4 Water balance equation.

Fig. 0.5 Waste does not need to be discarded. In Nepal there is a plant that uses faecal sludge from the local wastewater treatment plants to produce irrigation water, compost and biogas fuel. Simple digesters, sand filters and settlement tanks are used on a hillside location to produce useful products with minimal additional energy.

Fig. 0.6 Global releases to the world oceans. IUCN4. Contribution of different pathways to the release of microplastics. (Source: Boucher, J. and Friot D. (2017). Primary Microplastics in the Oceans: A Global Evaluation of Sources. Gland, Switzerland: IUCN. 43pp. Fig. 6.).

These complex chemicals, artificial fibres, medications and other contaminants are difficult to completely eliminate from wastewater. Therefore, residual amounts end up in water bodies and the natural environment. Studies have shown that these can potentially have an impact on marine and wildlife as well as the ecosystems that support them. Thus, it would be better if contaminants were removed before entering the drainage system. This can be achieved through public awareness, behaviour change and good design.

Therefore, other ‘man-made’ cycles should be acknowledged in the natural water cycle. These should be taken into consideration in the design of any building drainage system. Figure 0.7 shows some important design considerations depending on location and context.

Fig. 0.7 Interconnected water cycles.

Brief History of Drainage Systems

Since the beginning of time, rain from the sky has flowed overland and through the soil to rivers that lead to the sea. As civilizations developed, the rivers and nearby water bodies were utilized as disposal points for human waste and unwanted surface water, and sadly also for drinking water. As cities emerged, the open streams and ditches were covered and ‘underground drains’ created. Eventually, such drains were increasingly connected, enlarged and lined with brick or stone to produce a recognizable drain and sewer network.

This process took place in various parts of the world at different times. One of the earliest sewerage systems has been found to date back to about 4000 BC in Babylon. It was used for removing stormwater from the cities. The Orkney Islands in the north of Scotland provides the example of an early foul water drainage system. Here, the total system only served about six dwellings, so it was not very extensive, but it was created around 3200 BC. At around the same time, some far larger systems were being developed in and around India.

One of the earliest recognized drainage systems was discovered in Asia in the Indus valley. Estimated to have been built around 2350 BC, the city of Lothal had an extensive drain and sewer system that included cesspits. Cities in the area were also built with sophisticated water supply systems and baths. It has been reported that they used rainwater harvesting systems and practised irrigation using wastewater.

Perhaps the most sophisticated wastewater systems of the time belonged to the Minoans on the island of Crete, which were used from around 3000 BC to 1000 BC. They utilized spigot and socket joints in earthenware pipes that were sealed using cement. They had flush toilets and practised rainwater harvesting.

The Romans were famous for their water supply and underfloor heating systems. Their sewer systems date back to around 800 BC. The purpose was mainly for surface water and marshland drainage, which evolved to remove human waste by 600 BC. However, houses were not connected to sewers in Rome until about 100 BC, so progress was rather slow.

Iron pipes were created in Germany during the fifteenth century to transport water and wastewater. John Harrington invented the flush toilet in England in the sixteenth century. Even though it was reported that the king had a sewer installed at the palace to take waste from the kitchen by the fourteenth century, it took until the seventeenth century before internal drainage systems were common in British castles and other buildings inhabited by the rich. However, in London, drain and sewer systems were evolving from the sixteenth to seventeenth centuries. Each area would develop its own system with no regard for any adjacent areas. King Henry VIII instigated a ‘commission of sewers’ to address this issue and gave people responsibilities for looking after and cleaning their local sewers. After the ‘Great Stink’ of 1858, a more radical solution to the problem of odour and pollution was sought urgently.

In the USA, it was not until 1728 that New York turned its open sewers into covered ones.

In the French capital, Paris, a series of cholera outbreaks in the 1830s resulted in the installation of large sewers between 1840 and 1890. These ‘Les egouts’ were so impressive that regular weekend boat tours were conducted. By the 1930s, the whole city had a combined sewer system installed.

This brings us to today. In many ways, drainage has not evolved or developed much over many centuries. However, with a growing population there is a need to ensure that not only is our drainage system efficient, but also safe. The European Commission released a press release that included this statement in 2018:

Water reuse in the EU today is far below its potential despite the fact that the environmental impact and the energy required to extract and transport freshwater is much higher. Moreover, a third of the EU’s land suffers from water stress all year round and water scarcity remains an important concern for many EU Member States. Increasingly unpredictable weather patterns, including severe droughts, are also likely to have negative consequences on both the quantity and quality of freshwater resources. The new rules aim to ensure that we make the best use out of treated water from urban wastewater treatment plants, providing a reliable alternative water supply. By making non-potable (not for drinking) wastewater useful, the new rules will also contribute to saving the economic and environmental costs related to establishing new water supplies.

The rules it refers to are for irrigation of agricultural land using wastewater. The press release goes on to show how an integrated policy for water and wastewater is being developed based upon global needs and aims to:

Alleviate water scarcity across the EU, in the context of adapting to climate change. It will ensure that treated wastewater intended for agricultural irrigation is safe, protecting citizens and the environment. The proposal is part of the Commission’s 2018 Work Programme, following up on the Circular Economy Action Plan, and completes the existing EU legal framework on water and foodstuffs. It complements the ongoing modernization of the European economy, the Common Agricultural Policy and climate change ambitions, and contributes to reaching the UN Sustainable Development Goals in the EU (in particular Goal 6 on water and sanitation), as well as fitting into the transition towards a Circular Economy which is an important goal of the Commission.

Thus, it appears that there are now policy drivers to ensure the integrated drainage design is considered with all other aspects of water to meet the needs of the planet and not just our local environment.

The Drainage Chain

Water drainage can be defined as the safe and efficient removal of water and effluent from the point of origin to point of disposal without compromise to the health and safety of people in and around the building. Drainage systems help to deliver public health, minimize flooding and reduce contamination of the built environment.

Therefore, drainage in and around buildings serve three main purposes:

•To manage rainwater that falls on the roof

•To manage surface water on the ground around the site

•To manage foul/wastewater generated from inside the building.

Fig. 0.8 A typical drainage configuration.

Adequate site drainage is also needed to manage surface water; to avoid flooding as well as foul water encroachment. However, the process of doing this is not always straightforward. For example, there are currently about eighty-nine British Standards (BSs) relating to drainage! It will not be possible to cover all of this in this book. Therefore, the main regulations and standards will be signposted and the next chapter will cover the main design principles. But first, useful definitions:

•Domestic wastewater: water discharged from kitchens, laundry rooms, lavatories, bathrooms, toilets and similar facilities.

•*Drain: Typically, underground clay or plastic pipes that are used to carry wastewater from a source to a sewer network, and subsequently for treatment.

•*Drainage system: a connected natural or artificial network of pipes used to transport wastewater away from the source to final treatment or disposal sites.

•*Effluent or trade effluent: term used to describe wastewater from industrial activity.

•Foul water: wastewater from toilet, sinks, washing machines, dishwashers, etc..

•Lateral drain: sewer including ancillaries (access chambers, manhole, etc.) which serves a single property but lies outside that property’s boundary, i.e. within or beneath another property boundary or the street.

•*Wastewater: water-composed by-product from domestic and non-domestic buildings, surface water run-offs and other intentional or non-intentional water and sewerage discharge into natural or artificial drainage systems.

•Wastewater treatment: is a natural, chemical and/or biological process to make wastewater and effluent safe for reuse or safe discharge to the environment.

•Water recycling and reuse: occurs when wastewater is captured and/or treated to be used for other domestic or non-domestic purposes.

•Sewer: A sewer including ancillaries (access chambers, manhole, etc.) is defined as a drain that is shared or used by more than one property.

•*Surface water: naturally occurring water from rainfall and precipitation, which has not seeped into the ground and which is discharged to the drain or sewer system directly from the ground or from exterior building surfaces.

* Definitions sourced from BS EN 1085:2007, superseded by BS EN 16323:2014 Glossary of wastewater engineering terms. Definitions may be paraphrased.

Drainage systems are used to manage surface and subsurface water, as well as effluent originating from human, industrial and agricultural activities. Contemporary drainage systems and processes broadly consist of three stages: Capture (source processes), treatment and discharge/reuse (destination processes) (Figure 0.9).

Fig. 0.9 Water drainage stages.

Water Retention, Recycling and Reuse in the Drainage Chain

The introduction of water recycling and reuse into the drainage chain can make it a more sustainable process. The stages become circular, rather than linear, as shown in Figure 0.10. Further, the journey for wastewater is significantly shortened as most of this is collected, treated (as necessary) and retained or reused closer to the point of origin.

Fig. 0.10 Water drainage stages.

Studies and trials have argued for and against the economies of scale, cost-benefit, return on investment, customer/consumer buy-in, health risks, ease of use and maintenance, energy and carbon intensity and so on, of such systems. What is obvious is that there can be economic, environmental and social benefits to a more circular approach to localized or decentralized water systems in certain contexts or environment even if not applicable in all instances. Therefore, any worthwhile water and drainage design approach should consider water retention, recycling and reuse as part of a holistic water efficiency and resilience approach.

Alternative water supply and drainage systems will be discussed in more detail in subsequent chapters.

Drainage Standards and Regulations

An effective drainage system is important for public health as well as for environmental reasons. This book focuses on water drainage design at the building scale, it does not cover the disposal of industrial effluence or municipal transmission, treatment and disposal of wastewater. What is important to note is that there are important design, human/public health and environmental guidelines associated with each stage of the drainage chain. Therefore, different countries have different policies on drainage systems.

For example, in order to safeguard against contamination, infiltration into ground and surface water are not permitted in Austria. Such policies are understandable as there are continuous risks of man-made substances and other pollutants contaminating water sources. The impact of long-term accumulations of these pollutants and contaminants in water systems or the ramifications for the food chain and human health are still not fully understood. However, if most countries banned infiltration, the existing wastewater treatment infrastructure would not be able to cope without considerable investment in new treatment processes and plant solutions.

Other countries have regulations that limit the infiltration and discharge of wastewater into natural systems. Concerning buildings, such building regulations or codes tend to set minimum specifications that will ensure healthy and safe buildings. However, such regulations can be prescriptive and limit innovation. Hence, in a number of countries, the actual regulations can be rather vague, including such words as ‘adequate’, ‘sufficient’, ‘efficient’, ‘safe’, ‘comfortable’, ‘clean’, ‘hygienic’; all of which are rather subjective. Such generalized requirements are normally accompanied by examples of how to achieve the actual regulations. These are detailed in guidance documents that can be updated more easily and regularly than statutory legislation. Such documents often ‘call-up’ national, continental or international standards along with technical documents from industry to provide detailed specifications and rules.

An example is the building regulations of the regions of England, the largest country within the United Kingdom. (The building regulations for Wales and Northern Ireland tend to be similar to those of England, but the regulations in Scotland are based on a different legal system that can be more prescriptive). The Building Regulations (England) Part H: Drainage and Waste Disposal stipulates that an adequate drainage system should be provided to carry foul water from appliances in a building to a public or private sewer, septic tank or cesspool. Any septic tank should be correctly designed, built and located, and all paved areas should be adequately drained to avoid surface water problems. It also makes similar stipulations for the conveyance of rainwater from the roof of a building to a soakaway, an infiltration system, a water course or a sewer, except if the rainwater is being collected for reuse. As much as is feasible, rainwater drainage should be separated from foul water discharge. Only greywater from personal use and clothes washing can be collected for reuse in buildings. All drainage systems should have adequate access for continuation and maintenance, and should be located such that it does not harm people's health.

A number of international standards that emphasize the link between water supply and drainage systems are currently under preparation.

The approach taken by the ISO committee is identified in the extract quoted below from the current ISO 24511:2007 (Activities relating to drinking water and wastewater services — Guidelines for the management of wastewater utilities and for the assessment of wastewater services). This document sets out the role of drain and sewer systems and wastewater treatment and disposal:

Wastewater systems are built and operated mainly to protect public health and the environment. The type of wastewater system needs to be chosen and adapted in context with the density of the population, climatic conditions, environmental requirements for treatment and the technical/socio-economical ability of the responsible body to implement it, operate it and maintain it. It needs to be cost effective and sustainable, as well as permitting phased development to overcome the financial constraints while not compromising the stated objectives.

Fig. 0.11 The Building Regulations (England) Part H: Drainage and Waste Disposal.

Operationally, the broad objectives of a utility are to provide wastewater collection services on a continuous or at least intermittent basis (depending on the service mechanism chosen), meeting the related capacity requirements. Methods of wastewater treatment and/or disposal need to correspond to the chosen collection system.

Appropriately, treated wastewater is eventually returned to the environment and can have significant impact on both quantity and quality of natural water resources.

Effective and safe management of residues resulting from wastewater treatment, including their final disposal or reuse, is becoming increasingly important due to concerns about both environmental protection and resource conservation.

Since it often has a lifetime stretching over several human generations, wastewater infrastructure needs to demonstrate intergenerational equity. Consequently, a wastewater utility, regardless of ownership, is public in nature and will be subject to public scrutiny and policy. Other criteria, such as cost/affordability and service sustainability, are addressed in appropriate clauses of this International Standard.

To summarize, wastewater and drainage are not isolated. They are part of a global water cycle that until recently had generally been ignored. Historic drainage system designs tended to focus on managing local wastewater issues and assumed that the vastness of the planet’s oceans and soil could cope with whatever was disposed into them. The truth that most resources are finite and that an increasing population uses more resources has led to a re-evaluation of attitudes to waste and our stewardship of the planet. Local regulations are becoming more consistent across the planet and policies and strategies are being put in place internationally. Drainage is no longer simply a disposal route, but a conduit for different resources that can be utilized, reused and sensibly treated before re-entering the global water cycle. Perhaps we should reclassify ‘wastewater’ as ‘used water’, which better conveys that there should be no such thing as water that should be wasted.

PART ONE : OUTSIDE THE BUILDING

Chapter 1

WASTEWATER DRAINAGE SYSTEMS

This chapter discusses the evolution of site-based and municipal drainage systems and the importance of good drainage for public health and well-being. It also highlights the importance of good drainage design and the choice of appropriate methods for achieving both water efficiency and resilience. The second part of the chapter will present the main terminology, criteria and factors that inform ‘traditional’ drainage design in and around buildings and the built environment.

Here, building drainage system types and design considerations are discussed with particular focus on the collection and transmission of rainwater, foul and wastewater from buildings; commonly referred to as sewer systems. In the UK, sewer systems can be private and public, or separate and combined.

Useful standards and guidance documents include:

•BS EN 752 (2017) Drain and sewer systems outside buildings. Sewer system management (formerly seven parts, now only one part)

•BS EN 12056 Part 3 Gravity drainage systems inside buildings – Roof drainage, layout and calculation (although title is for ‘inside buildings’ the scope includes rainwater drainage attached to a building)

•EN 16933-2 (2018) Drain and sewer systems outside buildings – Design Part 2: Hydraulic design

•BS EN 1610 Construction and testing of drains and sewers

•BS EN 16932-1 (2018) Drain and sewer systems outside buildings. Pumping systems (In 3 parts including Vacuum systems and Positive pressure systems)

•BS EN 295 (2013) Vitrified clay pipe systems for drains and sewers (Currently in seven parts)

•BS 65 (1991) Specification for vitrified clay pipes, fittings and ducts, flexible mechanical joints for use solely with surface water pipes and fittings

•BS 4660 (2000) Thermoplastics ancillary fittings of nominal sizes 110 and 160 for below-ground gravity drainage and sewerage

•CIBSE Guide G (current version): Public Health & Plumbing Engineering.