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

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 TypeRunoff coefficient Notes G I Sheets> 0.9  Excellent quality water.  Surface is smooth and high temperatures help to sterilize bacteria. Tile (glazed)0.6 – 0.9  God quality water.  Unglazed can harbor moulds.  Contamination can exist in tile joints. Asbestos sheets0.8 – 0.9  New 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)0.2  Poor quality water  Little first flush effect  High turbidity due to dissolved organic material which does not settle.

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

SILT TRAPS

STORAGE TANKS Material a)Precast concrete b)Steel c)Plastic d)Ferro cement e)Bricks Shape  Sphere  CylindeR  Half sphere  Cube Location a)Above ground b)Underground

IDEALIZED TANK SHAPES ShapeNotes Sphere  Perfect 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. Cylinder  The 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 Sphere  A popular shape for underground tanks as the pit is easy to excavate and it is believed to have good material economies  Requires a large, free standing cover.  Underground tanks are simple to make with this shape using moldable materials. Cube  Perfect 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

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