EN896
REDUCING MAINS WATER USE
THROUGH RAINWATER HARVESTING
overview
COLLECTING A VALUABLE FREE RESOURCE AND REDUCING THE IMPACT OF RUNOFF
This leaflet targets
any business where
rainwater can be
collected in sufficient
volume to be re-used.
It details how to
quantify the volume
of rainwater that can
be collected and key
considerations, such
as water quality,
when assessing
options for re-use.
Installing rainwater harvesting
systems can provide a variety of
economic benefits, as well as
reduce the risk of flooding in
some areas.
TIP: It is more expensive
to retrofit rainwater
harvesting systems than to
invest in technology when the
site drainage system is under
construction.
Rainwater is ideal for many uses,
including cooling systems and
appliances, as there is a lower
concentration of salts to build up.
TIP: The re-use of
rainwater can improve
the overall BREEAM
performance for a building.
BREEAM (BRE Environmental
Assessment Method) is an
environmental assessment for
buildings (new and existing)
developed by BRE (Building
Research Establishment)
www.breeam.org/
If water requires treatment to a
high standard, cost and annual
maintenance will be higher than
a system requiring only low
quality water. Generally, the
systems with the fastest
payback periods utilise large
collection areas to supply a
constant demand of general
quality water. In certain
commercial installations, the
project payback can be as short
as 2-3 years.
REDUCING MAINS WATER USE THROUGH RAINWATER HARVESTING
Is rainwater harvesting suitable for you?
STEP 1
Quantify the amount of water
you currently use. This can most
easily be done by checking recent
water bills - it will probably be
useful to develop a spreadsheet
for your business with your water
consumption for different seasons
of the year. This will also allow you
to see the effects of rainwater
harvesting on your water costs.
STEP 2
Quantify the maximum water
you can harvest in a year using
the following equation:
Annual rainwater yield (Y) in m3
= P x A x 0.8
Where P = annual precipitation
(in metres); and,
A = collection area
(in square metres)
0.8 = typically, you should expect
to collect approximately 80% of
this water each year, due to small
losses in filtering and small rainfalls
that do not generate enough runoff.
The table opposite illustrates how
much water you could save based
upon your collection area. Annual
rainfall data can be obtained from
the Met Office website
(www.metoffice.gov.uk/climate/uk).
Example: With an average South
East rainfall of 0.6 metres, and a
roof area of 15 x 20 metres, you
could save almost £300 each year
in water and wastewater charges.
STEP 3
Storage - tanks and
pipework
Quantify the cost
Check your water bills to find out
how much you pay for water and
how much you could save by
using rainwater instead.
CONSIDERATIONS
Water quality
When considering rainwater
harvesting system installation,
water quality and its potential reuse must be considered. For
example, a food processing plant
may require large quantities of high
quality water, whereas water for
staff toilets and garden areas will
require less pre-treatment.
Once volume and required water
quality is known, you should
determine where to locate the
rainwater storage and consider
modifications to your existing
drainpipes.
TIP: If you are planning on
connecting the rainwater
system to existing plumbing, you
need to prevent any collected
water from accidentally pushing
back into the mains system.
Your plumber should be able to
advise you on the best location
to install sufficient backflow
protection.
Leicester City Council has
reduced the volume of mains
water used at Humberstone Golf
Course through rainwater
harvesting for irrigation.
Rainwater from the clubhouse is
collected and stored, before
being pumped onto greens mains water use has been
reduced by 20% and the
expected payback of the
system is 5 years.
Rainfall data UK
Rainfall (metres/year)
Y (m3)
Surface area (m2)
Will a rainwater harvesting
system provide benefits to your
business? Follow these steps to
find out:
0.4
0.6
0.8
1.0
1.5
2.5
100
32
48
64
80
120
200
200
64
96
128
160
180
400
300
96
144
192
240
360
600
500
160
240
320
400
600
1000
800
256
384
512
640
960
1600
1200
384
576
768
960
1440 2400
Envirowise Advice Line 0800 585794
|
www.envirowise.gov.uk
The UKRHA reports that annually,
over 400 rainwater harvesting
systems are installed in the UK.
With increasing water prices, the
feasibility of rainwater harvesting is
becoming more favourable. The
UK has fairly regular rainfall spread
during the year, meaning unused
space in storage tanks is reduced,
making UK rainwater harvesting
projects even more ideal.
Rainwater storage tank
Also consider safety of others; use
signs to indicate the quality of
water if available through a tap. If
appropriate, tap fittings that
cannot be interchanged with
standard town supply tap fittings
could be used.
TIP: Further information
can be found on the
WRAS (Water Regulations
Advisory Scheme) website
(www.wras.co.uk).
Running out of water need not be
a concern - a mains connection
will ensure that systems are
topped up when they get very low.
A large tank will give you more
capacity to store the water from
heavy downpours, increasing
savings, but cost more to
purchase. Also consider tank
location carefully; available options
include under or above ground.
Ideally, a balance should be found,
where water from the wettest time
of year is collected without tank
overflow. There are many
companies that can help you with
developing bespoke rainwater
harvesting systems: details can be
found on UK Rainwater Harvesting
Association (UKRHA) website.
Coolings Nurseries at
Knockholt near Sevenoaks in
Kent installed a rainwater
capture system which collects
7,000 m3 of rainwater each year.
The nursery now supplies almost
75% of its own water needs,
saving over £2,000/year. Runoff
onto neighbouring properties
has also been reduced, and
instances of flooding on site
have been drastically decreased.
Filtration unit
The table below identifies some common uses for rainwater
harvesting projects and associated treatments:
WATER USE
QUALITY REQUIRED
TREATMENT OPTIONS
• Nurseries, sports
grounds, gardens
• Toilet flushing
• Cooling (boilers)
• General cleaning
• Filter backwashing
LOW: Water is not used
for consumption, and
there is a very low risk of
contact. Water should
look clean and be odour
free.
• First flush diverted
• Coarse filter
• Laundry
• Cleaning of equipment
or process cleaning
MEDIUM: Water is not
used for consumption,
and there is a low risk of
contact. Water must be
clean and odour free, but
not necessarily sterile.
• All of the above, plus
• Fine filter (possibly
membrane filter)
• Food processing
• Cleaning food
processing equipment
• Substitute potable
supply
HIGH: Water may be
used for consumption,
water must be clean,
odour free and sterile.
• All of the above, plus
• Pathogen removal
and/or inactivation
(eg UV treatment)
Envirowise Advice Line 0800 585794
|
www.envirowise.gov.uk
Marshalls, a leading UK manufacturing company, implemented a
water and materials recycling system at its Ramsbottom site. Its
5,000 m2 roof-harvested rainwater was stored in two 40,000 gallon
tanks. This added nearly 3,000 m3 of water into the production
process. Along with other initiatives, the rainwater harvesting reduced
mains water consumption from 11,000 m3 to 500 m3. The whole
water-saving initiative cost £250,000, however, the total financial
saving from reduced water consumption, recycling materials, reduced
vehicle movements and disposal costs is estimated at £175,000 a
year, giving a payback period of just 15 months.
FURTHER INFORMATION
For further examples of projects in
the UK and internationally where
rainwater harvesting systems have
been successfully installed, or for
more advice on how rainwater
harvesting can impact your business
and the environment, see the
websites listed below:
The UK Rainwater Harvesting
Association www.ukrha.org
ENHANCED CAPITAL
ALLOWANCE
Examples of rainwater harvesting
and utilisation around the world
www.unep.or.jp/ietc/Publications/
Urban/UrbanEnv-2/9.asp
The Enhanced Capital Allowance
(ECA) scheme1 enables businesses
to claim 100% first year capital
allowances in investment in
rainwater harvesting equipment
named in the Water Technology
List.
The Water Regulations Advisory
Scheme www.wras.co.uk;
in particular the WRAS Information
and Guidance Note No 9-02-04
Reclaimed Water Systems:
Information About Installing,
Modifying or Maintaining Reclaimed
Water Systems
The following equipment is
supported:
Envirowise publications:
•
EN660 Reducing water use in
catering establishments
monitoring and control
equipment
•
rainwater filtration equipment
•
rainwater storage vessels
•
rainwater treatment equipment
Further information and advice can
be found at:
EN661 Reducing water use in
laundries
EN662 Understanding leaks, water
pressure and meters
Level detector
www.envirowise.gov.uk
www.eca-water.gov.uk
EN663 Reducing water use:
showers
EN664 Reducing water use in
washrooms: taps
EN665 Understanding water and
wastewater bills
EN666 Reducing water use in
washrooms: urinals
1
Developed by Defra and HM Revenue & Customs in partnership with Envirowise.
EN667 Reducing water use in
washrooms: WCs
Thank you to Stormsaver Ltd for help with the photography.
Prepared with assistance from Ashact, a Division of Hyder Consulting (UK) Limited.
Harwell | Didcot | Oxfordshire | OX11 0QJ | E advice@envirowise.gov.uk | www.envirowise.gov.uk
Envirowise - sustainable practices, sustainable profits. Envirowise is a Government-funded programme dedicated to putting the sustainable use of resources at the heart of business practice.
It is managed by AEA Technology plc and Serco TTI. Envirowise is funded by Defra, the Scottish Government, the Welsh Assembly Government and Invest Northern Ireland.
© Crown copyright. First printed July 2008. Printed on paper containing 80% recycled post-consumer fibre.
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