Rainwater Harvesting

A Practical Approach

Rashi Sharma

WHY HARVEST RAIN WATER???

A NATURAL RESOURCE PRESENTLY WASTED

PREVENTS GROUND WATER DEPLETION

A GOOD SUPPLEMENT TO PIPED WATER

POSITIVE COST TO BENEFIT RATIO

WATER CONSERVATION AND SELF DEPENDENCE

REDUCES “ECOLOGICAL FOOTPRINTS”

DOMESTIC ROOF WATER HARVESTING

COLLECTION

FILTERATION

STORAGE

USAGE

RECHARGE

HOW MUCH RAIN WATER CAN BE HARVESTED

Water harvesting potential

Water harvesting potential = Rainfall (mm) x Collection efficiency

Area of plot = 100 sq. m.

Height of the rainfall = 0.6 m )

Volume of rainfall over the plot = Area of plot x height of rainfall

Assuming that only 60 per cent of the total rainfall is effectively harvested

Volume of water harvested = 36,000 liters (60,000 liters x 0.6)

COMPONENT OVERVIEW

COMPONENT OVERVIEW

Typical Roof water Harvesting System in a Rural and an Urban Dwelling.

THE ELEMENTS

ROOF COLLECTOR GUTTERS & DOWNPIPES TRANSMITTERS FIRST RAIN SEPARATOR SEGREGATOR DRUMS FILTERS /

INTEMEDIATE STORAGE SILT TRAPS FILTER

CHAMBERS SUMPS AND OHT STORAGE

SYSTEMS BOREWELL, OPEN WELLS AND PERCOLATION PITS GROUND

WATER RECHARGE

COLLECTOR

Characteristics of roof types

Type Runoff coefficient

Notes

G I Sheets > 0.9Excellent quality water.Surface is smooth and high temperatures help to sterilize bacteria.

Tile (glazed) 0.6 – 0.9God quality water.Unglazed can harbor moulds.Contamination can exist in tile joints.

Asbestos sheets 0.8 – 0.9New sheets give good quality water.No evidence of carcinogenic effects by ingestion.Slightly porous so reduce runoff coefficient and older roofs harbor moulds and even moss.

Organic (Thatch) 0.2Poor quality waterLittle first flush effectHigh turbidity due to dissolved organic material which does not settle.

GUTTER

Water conveyance Q = A v = A 1/n R^2/3 S^1/2Interception

Gutter type a) Plastic b) Aluminum c) Steel d) Wood & Bamboo e) Half Pipe f) flexible guttering

Mounting

FILTERS AND SEPARATORS

Course leaf filtering

First flush diverters

Fine inlet filtering

In-tank processing

FILTERS AND SEPARATORS

FILTERS AND SEPARATORS

SILT TRAPS

TO SUMPØ 4"PVC PIPE

OVERFLOW PIPETO BOREWELL RECHARGE

6'-0"

Ø 3" PIPE

2'-6

"

6'-0"

40mm GRAVELFROM DOWN PIPES

3'-0

"

BAFFLEWALL

40mm GRAVEL

Ø 2" OVERFLOWPIPE

CHARCOAL

Ø 3" PIPE

BAFFLEWALL

STORAGE TANKS

Materiala) Precast concrete

b) Steel c) Plasticd) Ferro cemente) Bricks

Shape Sphere CylindeR Half sphere Cube

Locationa) Above groundb) Underground

IDEALIZED TANK SHAPES

Shape Notes

SpherePerfect spheres are only possible underground or partly underground however the shape can be approached using doubly curved surfaces.Good stress characteristics with little bending stress.All doubly curved structures need great skill or excellent tooling (or both) to manufacture reliably.Only suitable for moldable materials such as cement and clay or flexible materials such as some textiles and plastic sheeting.

CylinderThe most popular shape of water tanks.Hoop stresses are efficiently accepted, however a fixed joint between the tank wall and base will cause bending and sheer stresses near the joint.Suitable for use with either moldable materials or materials which can be bent on one direction (such as metal sheet)

IDEALIZED TANK SHAPES

Half SphereA popular shape for underground tanks as the pit is easy to excavate and it is believed to have good material economiesRequires a large, free standing cover.Underground tanks are simple to make with this shape using moldable materials.

CubePerfect spheres are only possible underground or partly underground.Bending stresses are high towards the corners.Very simple to construct using familiar house building techniques.Suitable for all materials including bricks and blocks.

PROS AND CONS OF ABOVE GROUND AND UNDERGROUND STORAGE

Above ground

Allows for easy inspection for cracks or leakage. Water extraction can be by gravity and extraction by tap. Can be raised above ground level to increase water

pressure. Require space. Generally more expensive. More easily damaged. Prone to attack from weather. Failure can be dangerous. Heavy vehicle driving over the cistern can also cause

damage.

PROS AND CONS OF ABOVE GROUND AND UNDERGROUND STORAGE

Under ground

Surrounding ground gives support allowing lower wall thickness and thus lower costs.

More difficult to empty leaving tap on. Require little or no space above ground. Water is cooler. Some users prefer it because it is like a well. Water extraction is more problematic – often requiring a pump, a long

pipe to a down hill location or steps. Leaks or failures are difficult to detect, Possible contamination of the tank from groundwater or floodwaters. The structure can be damaged by tree roots or rising groundwater. If the tank is left uncovered, children (and careless adults) can fall in

possibly drowning. If the tank is left uncovered animals can fall in contaminating the water. Heavy vehicle driving over the cistern can also cause damage.

STORAGE

GROUND WATER RECHARGE

STYLES OF RAIN WATER HARVESTINING

CLASSIFICATION

OCCASIONAL

INTERMITTENT

PARTIAL

FULL

USER REGIMES

Rainfall Quantity

Rainfall Pattern

Collection Surface Area

Storage Capacity

Daily Consumption Rate

No. of Users

Cost

Alternative Water Sources

Water Management Strategy

Thank You