Rain Water Harvesting

Why Harvest Rain Water

• Reduce ground water demand• Storage allows anytime use• Reduce flash-floods• Reduce erosion• Naturally clean• Naturally soft• Sustainable• Low Cost

Suitable if

• conservation already maxed-out • terrain is rugged or mountainous • water is too hard or mineral laden • lack of water security (potentially)• electricity & water prices are rising • groundwater is scarce (potentially)• population density is low (The Gambia)• seismic & flooding events are common • groundwater is contaminated (potentially)• consumers must restrict salt/chlorine intake • where availability is unreliable (The Gambia)• the aquifer is at risk of saltwater intrusion (potentially)

Uses – Non-potable

• Agriculture– Livestock– Crops– Gardens

• Cleaning– Laundry– Dishes– Bathing

Natural Solar Distillation

Simplest System

• Catchment area

Simple System

• Catchment area

• Distribution

Typical System

• Catchment area

• Screens

• Conveyance system

• Roof washer

• Storage

• Distribution

Complex System

• Catchment area

• Screens

• Conveyance system

• Roof washer

• Storage

• Purification

• Distribution

Catchment area

• Largest existing structures

• Non-organic roofs

• Metal corrosion

• Cost - none

Conveyance system

• Gutters or

• Water-tight fabrics

• Fasteners / brackets

• Screens

• Cost - low

Roof washer

• Diverts first flush– By volume – easiest– By rate - problematic

• Availability

• Cost - low

Storage

• Cistern– Concrete– Metal– Plastic

• For dry season

• Cost - highest

Sizing

• Cistern– 0.62 gallons / ft^2 (footprint) / inch (rain)– 75% - 90% efficiency– Use median rainfall data– Establish need

• Diversion Tank– Divert 10 to 50 gallons / 1000 ft^2

• Level of pollution

Questions?