Rainwater Harvesting

Submitted By:Gaurav Bhatt

1461567

INTRODUCTION Rainwater harvesting (RWH): technology used for collecting and storing

rainwater for human use from rooftops, land surfaces or rock catchments.

Rainwater is an important water source in many areas with significant rainfall but lacking any kind of conventional, centralised supply system.

Functions of rainwater harvesting

• providing water to people and livestock .

• providing water for food and cash crops .

• increasing groundwater recharge .

• reducing storm water discharges, urban floods and overloading of sewage treatment plants .

• reducing seawater ingress in coastal areas.

Types of Rainwater Harvesting Systems

1. Roof catchments• Simple roof water collection system for households• Larger systems for educational institutions, stadiums,

airports, and other facilities• Roof water collection systems for high-rise buildings in

urbanised areas

2. Ground catchments (man-made)

3. Rock catchments (natural, impervious outcrops)

4. Collection of storm water in urbanized catchments for recharge

Typical Domestic Rainwater Harvesting System

Ground Catchment System

Rock Catchment System

There are generally two methods of harvesting rainwater-

• Passive Rainwater Collection

• Active Rainwater Collection

Passive Rainwater Harvesting:

Passive Rainwater Harvesting is one of the oldest and easiest ways to harvest rainwater. Water is directed by earthen structures designed to transport and/or store rainwater. Passive systems are a hands-off approach used to send rainwater to beneficial areas of the landscape. This is also a way to redirect or control any problematic water that is collecting near a building or causing erosion issues.

Active Rainwater Collection• Active rainwater collection systems integrate a storage container, a tank or

cistern, into the system to catch rainwater runoff for later use on the property.

• These tanks can be installed above or below ground. Above ground systems usually rely on gravity to disperse the water and serve smaller areas.

• The in ground system requires a pump but can provide water throughout the site.

• In either case active systems bring a great advantage -- water can be stored and used when the soils are dry (instead of while the ground is soaked from the same rain that filled your tank).

• Active systems are also more complex than passive systems, cost more and require more maintenance.

Tank or Cistern. [ARC]

COMPONENTS OF A RAINWATER HARVESTING SYSTEM

A rainwater harvesting system comprises components of various stages - transporting rainwater through pipes or drains, filtration, and storage in tanks for reuse or recharge. The common components of a rainwater harvesting system

Catchments

Coarse mesh.

Gutters.

Conduits.

Catchments.• 1. Catchments: The catchment of a water harvesting

system is the surface which directly receives the rainfall and provides water to the system. It can be a paved area like a terrace or courtyard of a building, or an unpaved area like a lawn or open ground. A roof made of reinforced cement concrete (RCC), galvanised iron or corrugated sheets can also be used for water harvesting.

Coarse mesh.• 2. Coarse mesh at the roof to prevent the passage of debris.

Gutters.• 3. Gutters: Channels all around the edge of a

sloping roof to collect and transport rainwater to the storage tank.

Conduits.• 4. Conduits- Conduits are pipelines or drains

that carry rainwater from the catchment or rooftop area to the harvesting system. Conduits can be of any material like polyvinyl chloride (PVC) or galvanized iron (GI), materials that are commonly available

First Flush.`• First Flush Water Diverters improve water quality

and reduce tank maintenance by preventing the first flush of water, which may contain roof contaminants, from entering the tank. They help ensure cleaner water is  available for use, which protects rainwater pumps and internal household appliances such as clothes washing machines, toilets, hot water systems, etc.

collectiontank

screen

Filter.• The filter is used to remove suspended pollutants

from rainwater collected over roof. A filter unit is a chamber filled with filtering media such as fibre, coarse sand and gravel layers to remove debris and dirt from water before it enters the storage tank or recharges structure. Charcoal can be added for additional filtration.

Advantages of rain water harvesting

• Rainwater harvesting provides an independent water supply during regional water restrictions and in developed countries is often used to supplement the main supply.

• It provides water when there is a drought, can help mitigate flooding of low-lying areas, and reduces demand on wells which may enable ground water levels to be sustained.

• It also helps in the availability of potable water as rainwater is substantially free of salinity and other salts.

AVERAGE WATER COLLECTION• Example 1:

• For a building with a flat roof of size 10 m x 12 m in a city with the average annual rainfall of 800 mm

•

• Roof Area (A) = 10 x 12 = 120 m2

• Average annual rainfall (R) = 800 mm = 0.80 m

• Total annual volume of rainfall over the roof

• = A * R = 120 m2 x 0.80 m = 96 m3 = 96,000 litres

• If 70% of the total rainfall is effectively harvested,

• Volume of water harvested = 96,000 x 0.7 = 67,200 litres

• Average water availability = 67,200 / 365 ~ 184 litres/ day

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