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Caribbean Rainwater Harvesting Handbook

United Nations Environment ProgrammeP.O. Box 30552, Nairobi, KenyaTel: +254 2 621334

Fax: +254 2 624489/90Web: www.unep.org

Caribbean Environmental Health Institute (CEHI)P.O. Box 1111The Morne, Castries, St. LuciaTel: (758) 452-2501Fax: (758) 453-2721E-mail: [email protected]: www.cehi.org.lc



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Handbook for RainwaterHarvesting for the Caribbean

A practical guideline featuring best practices for

rainwater harvesting in small island Caribbeanenvironments

Prepared for UNEP by the Caribbean Environmental

Health Institute

October 2009


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Annex 3: Useful websites

Chennai Metro Water Rainwater Harvest ing ht tp : / /

www.chennaimetrowater.com/rainwatermain.htm

eToolkit on Rainwater Harvesting http://www.rainwater-toolkit.net/index.php?id=75

International Rainwater Catchment Systems Association (IRCSA)

http://www.eng.warwick.ac.uk/ircsa/

Rainwater Harvest ing ht tp : / /www.ra inharves t ing .com.au/

rain_water_harvesting.asp

Rainwaterharvesting.org http://www.rainwaterharvesting.org/

SearNet Southern and East Africa Rainwater Network http://www.searnet.org/searnetfinal/home.asp

Technology Informatics Design Endeavour (TIDE) http://www.tide-india.org/products/06polyhouse.html (example of RWH for agriculturalgreenhouse)

The Web of Rain - Online resources on rainwater harvestinghttp://www.gdrc.org/uem/water/rainwater/rain-web.html

YouTube videos on rainwater harvesting http://www.youtube.com/results?search_type=&search_query=rainwater+harvesting


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Caribbean Rainwater Harvesting Handbook Caribbean Rainwater Harvesting Handbook

5

Preface

This rainwater harvesting handbook is a practical guideline to assisthomeowners, contractors, architects, farmers, and business owners in

offering tips on how they can introduce rainwater harvesting to aug-

ment their water supply.

Access to a safe and reliable source of water still remains a number onedevelopment priority in the Caribbean. Over the past decades many coun-tries have made tremendous strides toward meeting this priority through theestablishment of centralized municipal water supply systems that service themajority of households and businesses. Only in the smallest islands, mostnotably the Grenadines and some of the Bahamas, rainwater remains the solesource of water. In several of the more arid islands such as Antigua &Barbuda, the Bahamas, and the Virgin Islands, rainwater harvesting is stillpractised in spite of access to the municipal potable supply, where residentson these islands still favour rainwater inmeeting their drinking and cookingneeds. In recent years however, someof the water-scarce countries have

made significant investments in desalini-zation technologies, where sea water isconverted to fresh water. In this case,the availability of a virtually unlimited supplyof water is now meeting the developmentneeds for water on these islands, but itcomes at a significant cost due to the energy inputs required among otherthings. On these islands, as well as on many others, with expanded access topotable water whether ground, surface or sea water, there has been a trend

to move away from RWH, due to the general perception that the practice isoutdated; to be relegated to a past era before the advent of the conventionalwater supply and distribution system.

The applications of RWH however are gaining prominence in national waterresources management planning. This is in the context of the pressures thatwater resources (both ground and surface sources) have been facing fromland degradation and pollution due to expanded urbanization, industrialization,agricultural and other commercial development. If pollution of the region's

waters is not addressed, climate change will exacerbate diminishing wateravailability at a more rapid pace. Rising sea levels will intrude vital coastal


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Mapping your roof areas - determining thecontribution catchments

Projecting the sloped roof area to horizontalcatchment area

The following are formulas to estimatethe areas of roof section shapes

Projecting the sloped roof area to horizontal catchment area- Sine of the roof angle; multiply by roof dimensions

Calculating the amount of water you cancapture off your roof

Quick Reference:


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Handbook is mainly based on single household applications, the con-

cepts can be applied or scaled up to other applications in agricultural,

commercial, industrial and municipal services sectors. Advice from pro-

fessional engineers, contractors or water services specialists should be solic-ited when investing in RWH systems.

Patricia AquingExecutive DirectorCaribbean Environmental Health Institute


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CEHI Caribbean Environmental Health Institute

Imp Imperial gallonhp horsepower

km3 cubic kilometers

m2 square metres

m3/d cubic meters per day

mg milligram per litre

ml millilitres

mm millimeters

PAHO Pan American Health Organization

PVC Poly-Vinyl Chloride

RWH Rain Water Harvesting

SIDS Small Island Developing States

SOPAC South Pacific Applied Geoscience Commission

UNEP United Nations Environment Programme

US$ United States dollars

USVI United States Virgin Islands

UV ultraviolet

Acronyms and units


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Rainwater harvesting can be used in a variety of municipal applications. Directroof capture off city buildings or capture of excess runoff from paved surfacescan be used to fill cisterns and other storage facilities that can be used forirrigation of green spaces and recreational facilities, washing and cleaning ofstreets and facilities, or for fire fighting.

Such bulk water storage can be used to augment emergency water suppliesfollowing natural disasters when the potable supply may be out of operation.

In this case filtration and treatment will need to be applied before distribution.Figures 33a and 33b show a few examples.

6. Non-domestic RWH applications

6.1 Municipal applications

Figure 33(A) Rainwater capture from a municipal facility in Charlotte Amalie, St. Thomas,USVI; 33(B) Rainwater harvesting for irrigation of Kensington Cricket Oval, St. Michael,Barbados (runoff from field and roof catchments diverted to perimeter sub-surface drain -see inset) (Photos courtesy: Henry Smith and Andrew Hutchinson)

(A) (B)

6.2 Agricultural applications

Crop irrigation and livestock watering have heavy water demands. In theCaribbean agricultural production is predominantly rain-fed with the excep-tion of larger commercial farm holdings where water is abstracted from irriga-tion drains, natural watercourses and wells. Under rain-fed production, cropyields will drop significantly during the dry season unless supplemental irriga-tion is applied. Livestock production is similarly impacted where water is in

short supply.


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Tree roots can intrude underground masonry including watertanks causing them to leak. Trees in close proximity to the watertanks should be pruned or cut to restrict advancement ofencroaching tree roots;

If mosquito breeding is observed in the tank (larvae present), it isbest to seek advice from your environmental health departmentfor assistance on control measures.

In the event when the water is contaminated by a dead animal, thetank should be drained immediately, cleaned, and disinfected withchlorine;

Monitor tanks for leaks and repair as needed;

Hygienically store and dispense water within the household. Usu-ally water collected from the storage tank is stored for shortperiods in small containers in the home. To protect the quality ofthis water:

Place storage containers out of reach of small childrenand animals

Keep containers covered or sealed Ensure containers are clean Draw water from containers in a hygienic manner.


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As with all water supply options, RWH has many advantages but there a fewdisadvantages that should be noted. The disadvantages may be minimized

with the adoption of a few simple water safety measures.

Advantages:

Rainwater harvesting provides a source of water at the point where it isneeded. It is owner-operated and managed;

It provides an essentialreserve in times of emer-gency and/or breakdown ofpublic water supply systems,particularly following naturaldisasters;

The construction of a rooftoprainwater catchment systemis simple, and these systems

can be built to meet almostany requirement;

Households can start with asingle small tank and addmore when they can affordthem;

Installation of concrete cisterns as part of the building foundation can

improve the structural integrity of the building substructure;

The physical and chemical properties of rainwater are often superior tothose of groundwater or surface waters;

Operating costs are low;

The construction, operation, and maintenance does not have to belabour-intensive;

Reduces runoff.

1.3 Rainwater harvesting the pros and cons

Figure 4 Domestic RWH system with cisternin St. Thomas (Source: H. Solomon and H. Smith, Univer-sity of the Virgin Islands)


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