REDUCING MAINS WATER USETHROUGH RAINWATER HARVESTINGCOLLECTING A VALUABLE FREE RESOURCE AND REDUCING THE IMPACT OF RUNOFF

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This leaflet targetsany business whererainwater can becollected in sufficientvolume to be re-used.It details how toquantify the volumeof rainwater that canbe collected and keyconsiderations, suchas water quality,when assessingoptions for re-use.

Installing rainwater harvestingsystems can provide a variety ofeconomic benefits, as well asreduce the risk of flooding insome areas.

TIP: It is more expensiveto retrofit rainwater

harvesting systems than toinvest in technology when thesite drainage system is underconstruction.

Rainwater is ideal for many uses,including cooling systems andappliances, as there is a lowerconcentration of salts to build up.

TIP: The re-use ofrainwater can improve

the overall BREEAMperformance for a building.BREEAM (BRE EnvironmentalAssessment Method) is anenvironmental assessment forbuildings (new and existing)developed by BRE (BuildingResearch Establishment)www.breeam.org/

If water requires treatment to ahigh standard, cost and annualmaintenance will be higher thana system requiring only lowquality water. Generally, thesystems with the fastestpayback periods utilise largecollection areas to supply aconstant demand of generalquality water. In certaincommercial installations, theproject payback can be as shortas 2-3 years.

Will a rainwater harvestingsystem provide benefits to yourbusiness? Follow these steps tofind out:

STEP 1Quantify the amount of wateryou currently use. This can mosteasily be done by checking recentwater bills - it will probably beuseful to develop a spreadsheetfor your business with your waterconsumption for different seasonsof the year. This will also allow youto see the effects of rainwaterharvesting on your water costs.

STEP 2Quantify the maximum wateryou can harvest in a year usingthe 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 expectto collect approximately 80% ofthis water each year, due to smalllosses in filtering and small rainfallsthat do not generate enough runoff.

The table opposite illustrates howmuch water you could save basedupon your collection area. Annualrainfall data can be obtained fromthe Met Office website(www.metoffice.gov.uk/climate/uk).

Example: With an average SouthEast rainfall of 0.6 metres, and aroof area of 15 x 20 metres, youcould save almost £300 each yearin water and wastewater charges.

STEP 3Quantify the cost

Check your water bills to find outhow much you pay for water andhow much you could save byusing rainwater instead.

CONSIDERATIONSWater quality

When considering rainwaterharvesting system installation,water quality and its potential re-use must be considered. Forexample, a food processing plantmay require large quantities of highquality water, whereas water forstaff toilets and garden areas willrequire less pre-treatment.

Storage - tanks andpipework

Once volume and required waterquality is known, you shoulddetermine where to locate therainwater storage and considermodifications to your existingdrainpipes.

TIP: If you are planning onconnecting the rainwater

system to existing plumbing, youneed to prevent any collectedwater from accidentally pushingback into the mains system.Your plumber should be able toadvise you on the best locationto install sufficient backflowprotection.

Envirowise Advice Line 0800 585794 | www.envirowise.gov.uk

REDUCING MAINS WATER USE THROUGH RAINWATER HARVESTING

Leicester City Council hasreduced the volume of mainswater used at Humberstone GolfCourse through rainwaterharvesting for irrigation.Rainwater from the clubhouse iscollected and stored, beforebeing pumped onto greens -mains water use has beenreduced by 20% and theexpected payback of thesystem is 5 years.

Is rainwater harvesting suitable for you?

Y (m3)Rainfall (metres/year)

2400

1600

1000

600

400

200

2.5

1440

960

600

360

180

120

1.5

960

640

400

240

160

80

1.0

768

512

320

192

128

64

0.8

576

384

240

144

96

48

0.6

384

256

160

96

64

32

0.4

1200

800

500

300

200

100

Sur

face

area

(m2 )

Rainfall data UK

Also consider safety of others; usesigns to indicate the quality ofwater if available through a tap. Ifappropriate, tap fittings thatcannot be interchanged withstandard town supply tap fittingscould be used.

TIP: Further informationcan be found on the

WRAS (Water RegulationsAdvisory Scheme) website(www.wras.co.uk).

Running out of water need not bea concern - a mains connectionwill ensure that systems aretopped up when they get very low.

A large tank will give you morecapacity to store the water fromheavy downpours, increasingsavings, but cost more topurchase. Also consider tanklocation carefully; available optionsinclude under or above ground.

Ideally, a balance should be found,where water from the wettest timeof year is collected without tankoverflow. There are manycompanies that can help you withdeveloping bespoke rainwaterharvesting systems: details can befound on UK Rainwater HarvestingAssociation (UKRHA) website.

The UKRHA reports that annually,over 400 rainwater harvestingsystems are installed in the UK.With increasing water prices, thefeasibility of rainwater harvesting isbecoming more favourable. TheUK has fairly regular rainfall spreadduring the year, meaning unusedspace in storage tanks is reduced,making UK rainwater harvestingprojects even more ideal.

Envirowise Advice Line 0800 585794 | www.envirowise.gov.uk

The table below identifies some common uses for rainwaterharvesting projects and associated treatments:

WATER USE QUALITY REQUIRED TREATMENT OPTIONS

• Nurseries, sportsgrounds, gardens

• Toilet flushing• Cooling (boilers)• General cleaning• Filter backwashing

LOW: Water is not usedfor consumption, andthere is a very low risk ofcontact. Water shouldlook clean and be odourfree.

• First flush diverted• Coarse filter

• Laundry• Cleaning of equipment

or process cleaning

MEDIUM: Water is notused for consumption,and there is a low risk ofcontact. Water must beclean and odour free, butnot necessarily sterile.

• All of the above, plus• Fine filter (possibly

membrane filter)

• Food processing• Cleaning food

processing equipment• Substitute potable

supply

HIGH: Water may beused for consumption,water must be clean,odour free and sterile.

• All of the above, plus• Pathogen removal

and/or inactivation (eg UV treatment)

Rainwater storage tank

Filtration unit

Coolings Nurseries atKnockholt near Sevenoaks inKent installed a rainwatercapture system which collects7,000 m3 of rainwater each year.The nursery now supplies almost75% of its own water needs,saving over £2,000/year. Runoffonto neighbouring propertieshas also been reduced, andinstances of flooding on sitehave been drastically decreased.

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.

This material may be freely reproduced in its original form except for sale or advertising purposes.

ENHANCED CAPITALALLOWANCE

The Enhanced Capital Allowance(ECA) scheme1 enables businessesto claim 100% first year capitalallowances in investment inrainwater harvesting equipmentnamed in the Water TechnologyList.

The following equipment issupported:

• monitoring and controlequipment

• rainwater filtration equipment

• rainwater storage vessels

• rainwater treatment equipment

Further information and advice canbe found at:

www.envirowise.gov.uk

www.eca-water.gov.uk

FURTHER INFORMATIONFor further examples of projects inthe UK and internationally whererainwater harvesting systems havebeen successfully installed, or formore advice on how rainwaterharvesting can impact your businessand the environment, see thewebsites listed below:

The UK Rainwater HarvestingAssociation www.ukrha.org

Examples of rainwater harvestingand utilisation around the worldwww.unep.or.jp/ietc/Publications/Urban/UrbanEnv-2/9.asp

The Water Regulations AdvisoryScheme www.wras.co.uk;in particular the WRAS Informationand Guidance Note No 9-02-04 Reclaimed Water Systems:Information About Installing,Modifying or Maintaining ReclaimedWater Systems

Envirowise publications:

EN660 Reducing water use incatering establishments

EN661 Reducing water use inlaundries

EN662 Understanding leaks, waterpressure and meters

EN663 Reducing water use:showers

EN664 Reducing water use inwashrooms: taps

EN665 Understanding water andwastewater bills

EN666 Reducing water use inwashrooms: urinals

EN667 Reducing water use inwashrooms: WCs

Marshalls, a leading UK manufacturing company, implemented awater and materials recycling system at its Ramsbottom site. Its5,000 m2 roof-harvested rainwater was stored in two 40,000 gallontanks. This added nearly 3,000 m3 of water into the productionprocess. Along with other initiatives, the rainwater harvesting reducedmains water consumption from 11,000 m3 to 500 m3. The wholewater-saving initiative cost £250,000, however, the total financialsaving from reduced water consumption, recycling materials, reducedvehicle movements and disposal costs is estimated at £175,000 ayear, giving a payback period of just 15 months.

1 Developed by Defra and HM Revenue & Customs in partnership with Envirowise.

Thank you to Stormsaver Ltd for help with the photography.

Prepared with assistance from Ashact, a Division of Hyder Consulting (UK) Limited.

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