Rain Water Harvesting. what shoud do?

Civil Engineering Water & Harvesting


  What is rain water harvesting ?

  • It is the activity of direct collection of rain water
  • Rain water can be stored for direct use or can be recharged into the ground water aquifer
  • Rain Water Harvesting RWH- process of collecting, conveying & storing water from rainfall in an area – for beneficial use.
  • Storage – in tanks, reservoirs, underground storage- groundwater

Rain water harvesting techniques:-

There are two main techniques of rain water harvestings.

  • Storage of rainwater on surface for future use.
  • Recharge to ground water.

Rain Water Harvesting– Advantages:-

  1. Provides self-sufficiency to water supply
  2. Reduces the cost for pumping of ground water
  3. Provides high quality water, soft and low in minerals
  4. Improves the quality of ground water through dilution when recharged
  5. Reduces soil erosion & flooding in urban areas
  6. The rooftop rain water harvesting is less expensive & easy to construct, operate and maintain
  7. In desert, RWH only relief
  8. In saline or coastal areas & Islands, rain water provides good quality water

 Rain water harvesting parts :-

  • Roof catchment
  • Gutters
  • Down pipe & first flushing pipe
  • Filter Unit
  • Storage Tank

 Roof catchment:-

The roof of the house is used as the catchment for collecting rain water. The style construction and material of the roof effect its suitability as a catchment, Roofs made of corrugated iron sheet , asbestos sheet, Tiles or Concrete can be utilized for harvesting the rain water.


Gutters are channels fixed to the edges of roof all around to collect & transport the rainwater from the roof. Gutters can be made in semi-circular and rectangular shape with cement pipe, plain galvanized iron sheet, PVC pipes, bamboos etc. Use of locally available material reduce the overall cost of the system.

 Down Pipe:-

It is the pipe which carries the rainwater from the gutters to the filter & storage tank. Down pipe is joined with the gutters at one end & the other end is connected to the filter unit of the storage tank. PVC or GI pipe of 50mm to 75mm (2 to”) are commonly used for down pipe. Bamboo can be also used wherever available and possible

First Flush Pipe:-

Debris, dust & dirt collect on the roof during non rainy periods when the first rain arrive. A first flush system arrangement is made to avoid the entering unwanted material into the Filter media & storage tank. This is a simple manually operated arrangement or semi-automatic system with a valve below the ‘T’ junction

 Filter Unit:-

The filter unit is a container or chamber filled with filter media such as coarse sand, charcoal, coconut fiber, pebbles & gravels to remove the debris & dirt from water that enters the tank. The filter unit is placed over the storage tank or separately. It may be of Ferro cement filter unit, Aluminum, Cement rings or Plastic bucket etc.

 Storage Tank:-

It is used to store the water that is collected from the roof through filter. For small scale water storage plastic buckets, jerry cans, clay or cement jars, ceramic jars, drums may be used. For larger quantities of water, the system will require a bigger tank with cylindrical or rectangular or square in shape constructed with Ferro cement or cement rings or plain cement concrete or reinforced cement concrete or brick or stone etc. The storage tank is provided with a cover on the top to avoid the contamination of water from external sources. The storage tank is provided with pipe fixtures at appropriate places to draw the water to clean the tank & to dispose of extra water. A provision for keeping the vessel to collect the water is to be made.

 Solar Thermal Energy:-

Solar Water Heating

  • Solar water heating is the most efficient and economical use of solar energy

 How Does it Work?

  • Systems can be passive or active
  • Passive systems only found in warmer climates, as they are prone to freezing
  • Active: Roof-top collectors heat glycol which then passes through a heat exchanger in the storage tank to heat water
  • Electric pump can be run on solar PV

Solar Photo voltaic Systems:-

  • Photovoltaic (PV) systems convert light energy directly into electricity.
  • Commonly known as “solar cells.”
  • The simplest systems power the small calculators we use every day. More complicated systems will provide a large portion of the electricity in the near future.
  • PV represents one of the most promising means of maintaining our energy intensive standard of living while not contributing to global warming and pollution

How Does it Work?

  • Sunlight is composed of photons, or bundles of radiant energy. When photons strike a PV cell, they may be reflected or absorbed (transmitted through the cell). Only the absorbed photons generate electricity. When the photons are absorbed, the energy of the photons is transferred to electrons in the atoms of the solar cell.
  • Solar cells are usually made of two thin pieces of silicon, the substance that makes up sand and the second most common substance on earth.
  • One piece of silicon has a small amount of boron added to it, which gives it a tendency to attract electrons. It is called the p-layer because of its positive tendency.
  • The other piece of silicon has a small amount of phosphorous added to it, giving it an excess of free electrons. This is called the n-layer because it has a tendency to give up negatively charged electrons.


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