Table Of ContentBNWAT05: Rainwater & greywater
systems - Supplementary briefing
note
Version 1.0
This Briefing Note and referenced information is a public consultation document and
will be used to inform Government decisions. The information and analysis forms
part of the Evidence Base created by Defra‟s Market Transformation Programme.
1 Introduction
Rainwater harvesting (RWH) and greywater reuse systems provide non-potable supplies of
water to buildings. By providing an alternative source of water they can help new and
existing buildings reduce demand for mains water supply. These standards may be imposed
by regulatory or local planning requirements. However, the feasibility of these systems in
new and existing buildings must be considered fully prior to development.
The information in this note is for England and Wales as Defra and Welsh Assembly
Government policies and actions may not be applicable in Scotland and Northern Ireland.
The information may be used to inform feasibility studies.
1.1 Purpose of the briefing note
This briefing note defines rainwater harvesting and greywater reuse system technologies
and presents the barriers and opportunities to increased uptake. This note is consistent with
other water sector Market Transformation Programme (MTP) briefing notes by focusing on
domestic households, but also considers the non-household sector. The overall purpose of
this briefing note is to increase uptake of rainwater and greywater systems in situations
where these are technically and financially feasible. It aims to do this by providing the key
facts on both of these technologies: definitions; product types and performance; best
practice installations and yield methodologies; availability and pricing; applicability in
different building types; and future changes in product and policy development.
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1.2 MTP Goals
Sustainable water management is essential to protect the water environment and to meet
current and future demands for water. The key to water efficiency is reducing waste, not
restricting use.
At present, most buildings are supplied with potable water (i.e. wholesome water fit for
drinking) from the public water supply network. Much of this is used in activities where non-
potable water would suffice. For example, in many existing homes, toilet flushing is
estimated to account for around 30 per cent of the household‟s daily demand (although data
1
from water companies indicates that this average is falling to 26 per cent as more new
homes are built to higher standards of water efficiency and older WCs in exis ting homes are
replaced with lower flush models). In non households toilet flushing may be a much higher
proportion of domestic - type demand.
1.3 Content of the briefing note
This briefing note contains the following information:
Section Information
1: Introduction 1.1 Purpose
1.2 Goals
2: Drivers 2.1 Water availability
2.2 Housing growth
2.3 Building Regulations and the Code for Sustainable Homes
2.4 Surface water management
3: Definitions Definitions and terminology
4: Water use in the home 4.1 How much can be saved
5: Product standards 5.1 BSI Rainwater code of practice
5.2 BSI Greywater code of practice
5.3 Related water regulations
6: Determining feasibility 6.1 Building characteristics
6.2 Economic Factors
6.3 Social Factors
6.4 Opportunities and barriers
7: Sustainability Energy and carbon
8: Innovation Integrated systems
9: Recommendations and Actions to increase uptake, actions to improve MTP data
action plans
Appendix A Product descriptions
Appendix B Environmental benefits
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BNWAT01 WCs:Market projections and product details
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2 Drivers
2.1 Water Availability
Annual average rainfall in England and Wales varies between less than 700 mm to over
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2000 mm per year . Whilst this is plentiful in some areas (e.g . the north and west of the
country), these rainfall totals have to be put in the context of the d emand for water from a
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population of approximately 54.8 million .
The total volume of water that is abstracted every day by the water companies in England
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and Wales is 14,449 Ml/d . Two thirds of this (approximately 75 per cent) is supplied to
househol ds and non households, and the vast majority of this is for domestic use.
However, water is a finite resource and three factors are increasing the pressure upon
existing water resources:
The population is expected to continue growing, particularly in the south-east of
England and there is a trend towards single occupant dwellings. This has been shown
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to increase pcc ;
The impact of climate change which UK Climate Projections predicts will reduce
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summer rainfall and which may at the same time increase c limate influenced
de mands, such as personal washing; and
Increasing availability of more consumptive water using products such as power
showers, and consumptive behaviours, e.g. increased personal washing. Water
companies‟ Water Resource Management Plans contain strategies specifically aimed
at trying to reduce per capita consumption (pcc). Several water companies have
reported pcc levels that are far above 150 litres per day.
2.2 Housing growth
Significant housing growth is planned for the next 10 to 15 years. The number of households
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in England is projected to grow to 27.8 million in 2031 , and to a total of 29 .2 million in
England and Wales, an increa se of 6.3 million (29 per cent) over the 2006 estim ate , or
252,000 households per year. This has the potential to increase the demand for potable
water. In particular, development in the south and east will add significant pressure on water
supply in the most water - stressed region of the country.
2
http://www.metoffice.gov.uk/corporate/library/factsheets/factsheet09.pdf
3
http://www.statistics.go v.uk/statbase/Product.asp?vlnk=15106
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Water UK Water Supply and Infrastructure Data http://www.water.org.uk/home/resources - and -
links/waterfacts/waterindustry/data
5
Herrington (1996). Climate change and the demand for water.
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UK Climate Projections 2009. Online climate change projections report.
http://ukclimateprojections.defra.gov.uk/content/view/2068/500/
7
http://www.communities.gov.uk/documents/statistics/pdf/1172133.pdf
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More detail on population and housing growth forecasts is available in BNWAT06: Domestic
water use in new and existing buildings.
2.3 Building Regulations (Part G) and the Code for Sustainable
Homes
The Code for Sustainable Homes and the 2009 amendment to the Building Regulations set
whole building consumption standards for new homes. Part G of Schedule 1 of the Building
Regulations (2000) stipulates that in new dwellings:
“reasonable provision must be made by the installation of fittings and fixed appliances
that use water efficiently for the prevention of undue consumption of water”.
Regulation 17K specifies:
“the potential consumption of wholesome water by persons occupying [the new]
dwelling must not exceed 125 litres per person per day..,[calculated according to the]
Water Efficiency Calculator for New Dwellings”.
The revised Building Regulations are in-line with Level 1/2 of the Code for Sustainable
Homes, with an allowance of five litres per head per day for external use:
Level 1/2 for water is defined as 120 litres/person/day;
Level 3/4 for water is defined as 105 litres/person/day; and
Level 5/6 for water is defined as 80 litres/person/day.
It is generally accepted that achieving level 3/4 of the Code for water can be achieved by
installing an appropriate combination of water efficient fixtures and fittings, and continuing to
influence consumer behaviour. It does not require installation of rainwater or greywater
systems and the cost to deliver a new home to CSH level 3/4 could be approximately £125
per house above the cost of construction of a house to meet the CSH Level 1/2 performance
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standard of 120 l/h/d (CLG, 2008 ). What is important is that achieving CSH level 5/6
standard of 80 litres per head per day (or lower) is likely to require some form of non - potable
water input to domestic properties, e.g. harvested rainwater or reused greywater .
Future developments, particularly in the most water stressed parts of England and Wales,
may require new households to be designed and built to achieve consumpti on rates at level
5/6 of the Code for Sustainable Homes (80 litres per head per day). T his level of water
efficiency is very likely to require some form of rainwater harvesting or greywater reuse. The
nature and design of such systems will depend on wide number of factors, and the success
of these systems will require co - operation from a large number of stakeholders, including
planners, developers, water companies, and others.
8
CLG (2008). Cost Analysis of The Code for Sustainable Homes. Final Report
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2.4 Surface water management
In addition to water resources issues, there are also concerns about rainwater drainage from
urban areas. Planning authorities are required to consider the effects of development on
surface water drainage and the potential impact on flood risk, (Planning Policy Statement
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25 ) . The suitability and sustainabi lity of developments will increasingly be judged, in part,
on their requirements for water supply and wastewater removal. Rainwater harvesting has
the potential to provide benefits in the form of attenuating rainfall and minimising surface
water run - off. Further, BRE, which manages the Code on behalf of Communities and Local
Government, has issued guidance that includes consideration of the use of rainwater
harvesting systems to contribute to surface water management, “where infiltration cannot
reduce all of the additional volume [surface water] ….. must evaluate the appropriateness of
rainwater harvesting systems to reduce the residual additional volume by diverting water for
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use within the dwelling” .
Further information on environmental benefits of rainwater harvesting and greywater reuse is
provided in Appendix B.
9
http://www.communities.gov.uk/publications/planningandbuilding/pps25floodrisk
10
BRE (2009). Code for Sustain able Homes – Technical Guidance Note 001 Supplementary
guidance on the assessment of the Management of Surface Water Runoff criteria (SUR 1).
http://www.breeam.org/filelibrary/Sur__1__Guidance_note__v12__2_.pdf
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3 Definitions
Wholesome water means water complying with the requirements of regulations made under
Section 67 (standards of wholesomeness) of the Water Industry Act 1991.
Non wholesome water means water that does not meet the requirements for wholesome
water, but is considered suitable for certain applications having regard to the risks to human
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health. This could include greywater or harvested rainwater .
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Rainwater is that arising from atmospheric precipitation .
Rainwater harvesting
The principle of rainwater harvesting is that rainwater is collected from roof areas and/or
areas of hard-standing, treated as appropriate, then pumped, direct or via a header tank, to
or within individual buildings. This water can be used without disinfection for non-potable
applications such as toilet flushing, outside water use, and non-hygiene cleaning. It can be
used for washing machines, although there may be occasional colour and odour issues,
depending on the quality of water collected. A mains supply must be provided for when
there is no rainwater in the storage tank.
Water butts are useful simple systems to provide water for gardens but these are not
included within the MTP definition of a rainwater harvesting system.
Greywater is domestic wastewater excluding wastewater arising from the WC. It is generally
collected from baths, showers and washbasins and may also be collected from kitchen
sinks, although the level of contamination from foodstuffs and other sources usually preclude
the use of kitchen wastewater. After basic treatment, greywater may be used for purposes
around the home such as toilet flushing or garden watering that do not require water of
potable water quality.
Greywater reuse is the use of untreated greywater for purposes that do not require potable
water.
Reclaimed water
Unlike greywater, reclaimed water is that which has not been supplied via the mains, e.g.
untreated borehole water. It is collected and treated for specific non-potable uses such as
flushing WCs.
SuDS
Sustainable drainage measures which alleviate flood risks both at a development site and
elsewhere in the catchment.
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Building Regulations Part G General Guidance
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BS 8515: 2009 . Rainwater harvesting systems – Code of practice.
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4 Water use in the home
When considering the implementation of alternative supply systems within new buildings it is
important to understand domestic water use patterns. Data on household water use is
available in the water company Water Resource Management Plans. Figure 4.1 represents
the average data from those water companies that have undertaken customer use surveys
and other forms of data collation.
It shows that toilet flushing is the largest single use of water (26 per cent of total demand),
with personal washing (showers, baths and taps) accounting for a further 42 per cent.
Washing machines also account for a significant percentage of the total volume at 10 per
cent. The remaining third is consumed via washing up in kitchen sinks (7 per cent), outdoor
use (9 per cent), and other miscellaneous uses (6 per cent).
As defined in Section 1.2, rainwater is suitable for uses that do not require potable water
quality such as WC flushing and outside use (in total approximately 35 per cent of household
use). Greywater is suitable for WC flushing.
Figure 4.1 Water use in the home
Car washing,
Miscellaneous
1%
Source: Musicer,o 6-%component data from the water companies 2009 Water Resource
Management Plans.
Garden use, 8%
Toilet flushing,
26%
4.1 How much water can be saved
Dish washing,
7%
The environmental drivers for saving water and reducing demand for mains supplies are
clear. The question is;
Clothes
washing, 10%
How much water can be saved through rainwater harvesting and greywater reuse?
Bath use, 14%
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Shower use,
19%
On average, each person in England and Wales uses just over 150 litres of mains drinking
quality water every day, so a family of four uses around 220,000 litres per year. In theory, of
this average mains water use, approximately 44 per cent is used for WC flushing, supplying
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the washing machine and watering the garden . This mains water usage could be
substituted with harvested rainwater or treated greywater. There are some concerns over the
use of harvested rainwater for clothes washing mainly that the quality of the water could
damage clothes but these are not prohibitive and may be resolved.
7,599 Ml of potable water is supplied to households in England and Wales each day and up
to one third of this is used to flush toilets. Savings are highly dependent on supply being
sufficient to meet demand and uptake, rainfall patterns, coll ection systems, and personal
habits (particularly for greywater reuse) will limit the maximum potential from being realised.
However, i f just one per cent of all homes used an alternative source of water to flush the
toilet 22.8 Ml/d of water would be sav ed.
Rainwater can be used to flush toilets and wash clothes if there is sufficient yield and
storage capacity. This is dependent on rainfall and how much of this can be collected and
so savings may vary throughout a year. The installation of a greywater reuse system should
provide more than adequate supply for toilet flushing, and potentially save 20 per cent of
internal household use, in a house already fitted with a highly water efficient WC (e.g. 4.5
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litre single flush, or 4/2.6 litre dual flush toilet ) .
4.1.1 Calculating water demand and yield of non-potable technologies
Rainwater harvesting is a simple concept. Rainwater is channelled directly from the
surface(s) it falls on. Once collected and stored it can be used for non -potable purposes.
From a holding tank from the water is fed to the point of use, either by gravity (if the tank is
stored at a level above the point of use), or by a small pump. The v olume required is a
function of the demand for non-potable water.
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CIRIA and the Environment Agency have published guidance on how demand and yield
for rainwater harvesting systems should be calculated. The recomm ended formula is
presented below:
2
Annual rainfall (mm) x effective collection area (m ) x drainage coefficient (%) filter
efficiency (%) x 0.05
(Environment Agency (2010). Harvesting rainwater for domestic uses: an information guid)e.
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Analysis of water company 2009 Water Resource Management Plan micro-component data (survey
based)
14
London Development Agency (2009). Managing Water - Reducing Water Demand. Technica l
Report (Entec, unpublished).
15
CIRIA (2001) Rainwater and Greywater Use in Buildings: Best Practice Guidance. Report C539.
CIRIA, London
16
Environment Agency (20 10 ). Harvesting rainwater for domestic uses: an information guide.
Environment Agency. Br istol
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This calculation takes account of:
Annual rainfall totals and the temporal variation in rainfall in the specific site location;
2
The effective collection area (m ) (equal to the area of roof and/or hard-standing that
can be reasonably used to collect rainfall);
A drainage coefficient (based on type of roof and other catchment materials, and the
proportion of actual rainfall that can be collected, allowing for surface wetting,
evaporation and excess runoff during intense storm events); and
Filter efficiency; of the water that is collected in the gutters not all will reach the
holding tank. (manufacturers usually advise that 90% of the water flowing into the
filter is retained).
The feasibility of greywater systems is independent of rainfall and less likely to be affected
by occupancy rate. However, it could be that occupants of a single in-house system use
only a small amount of water for bathing and spend the majority of the day at home,
therefore using a larger amount of water for flushing the toilet. This would create a higher
demand for treated greywater than the quantity available and would also lead to minimal
water savings.
Unlike rainwater systems which are heavily dependent on the dimensions of a building to
generate sufficient yield, and in general the feasibility of greywater is affected more by the
performance and perception of the technology. The following formula calculates the demand
and the yield of greywater systems:
Demand = per person daily average WC flush x occupants sharing greywater system
A second formula calculates the daily non potable supply (i.e. water from bath/shower)
Supply = per person personal washing demand* x occupants sharing greywater system
*Taken from the CSH Water Use Calc ulator
Feasibility assessments also need to consider the energy impacts of moving water around a
property for reuse.
4.1.2 Current Ownership
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Around 2000 rainwater harvesting systems were installed in the UK in 2006/07 an d by
2010 this is believed to have increa s ed ( there are no data for England and Wales
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specifically ) . Of these , 70 per cent were domestic systems . The majority (> 95 per cent)
17
Environment Agency (2008). Harvesting rainwater for domestic uses: an information guide.
Environment Agency. Bristol
18
Email communication, Rainwater Harvesting Association (October 2010).
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are sold for installation in new buildings. Retrofit rates are currently quite low since there are
few incentives to counteract the installation costs that are often prohibitive in existing
buildings. There may be some incentive from savings on water bills but these will only apply
to metered customers and may be limited due to the current low price per unit of water. One
of the main issues limiting retrofits is the physical constraint of accommodating a water
storage tank.
There has been a recent shift (2008-2010) in the types of developers who procure rainwater
harvesting systems from mainly self-builders and small developers to social housing
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contractors and major developers in the UK . This may demonstrat e that rainwater
harvesting is moving from the small - scale peripheral market to more mainstream
developments. Social housing is a development sector that offers large scale potential for
improving water efficiency. The Code for Sustainable Homes was developed using the
Building Research Establishment‟s (BRE) EcoHomes System, which had already achieved
success in reducing the impact of affordable housing projects, in particular within the social
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housing sector . Waterwise has also made recommendations for the Government to
include water efficiency in the Decent Homes initiative, particularly by recommending water
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efficient showers as a standard fitting . The Code for Sustainable Homes now r e quires new
social housing developments to meet level 3/4 for water.
19
Email communication (October 2010): SCP Environmental Ltd
20
CLG (2006). Code for Sustainable Homes . A step - change in sustainable home building practice.
http://www.planningportal.gov.uk/uploads/code_for_sust_homes.pdf
21
Waterwise (2009). Beyond Decent Homes. Memorandum. http://www.publications.parliament.uk
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