Rain water harvesting

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Today, as millions of people the world over do not have access to clean drinking water, tapping the clouds instead of the water pipes has become a significant way of conserving water and replenishing ground water levels. Rain water harvesting, collecting rain water in barrels or tanks and/or directing it to recharge ground water, is the simplest way to address the looming water crisis.

[edit] Why should I be aware of this?

Water is everyone's business. By harvesting rain, everyone will learn to value each raindrop. It makes perfect sense to utilize our natural resources and conserve water for our daily use. Rain water harvesting makes the maximum use of rain water, a free resource. Here are some of its obvious benefits --

  • It provides additional water for the city's requirement.
  • It increases soil moisture levels and promotes urban greenery.
  • It helps increase the ground water table through artificial recharge.
  • It mitigates urban flooding and improves the quality of ground water.

It has some more added benefits. Here are some --

  • A supply of oxygenated, un-chlorinated water which is good for plants.
  • Savings because of reduced water bills.
  • Availability of clean irrigation water.
  • Unlike municipal water that contains ammonia, fluoride and chlorine, rainwater is naturally soft and PH neutral.
  • Control of moisture levels around the foundation of the building.
  • Diversion of water from the municipal storm drain system.
  • Rivers and streams are protected from runoff pollution.

In certain areas it may not be possible to harvest rain water for drinking or cooking since pesticides from nearby factories or aerial spraying can pose health risks. However, even then, it can be used for flushing toilets and washing laundry. It can also be used for showering or bathing. Prior treatment will be needed only if it is to be used for drinking.

[edit] All about rainwater harvesting

There are a number of components used at various stages of rainwater harvesting. The stages are rainwater transportation through pipes or drains, filtration of the water, followed by storage in tanks for reuse or recharge. The common components of a rainwater harvesting system involved in these stages are given below:

  • Catchments: Rainfall is directly received on this surface and from here delivered to the system. It can be a terrace or a building courtyard, a lawn or open ground.
  • Coarse mesh: is installed on the roof to prevent passing of debris.
  • Gutters: these are channels on the edges of a sloping roof all around for collection and transportation of rainwater to the storage tank.
  • Conduits: These are pipelines or drains made of material such as polyvinyl chloride (PVC) or galvanized iron (GI). The pipelines are used for the purpose of carrying rainwater from the catchment or rooftop area to the harvesting system.
  • First-flushing: a valve to flush out the relatively larger amount of pollutants that come from the first spell of rain. Flushing out prevents entry of these elements into the system
  • Filter: This is a chamber consisting of filtering media such as fiber, coarse sand and gravel layers. They help remove debris and dirt from water before they enter the storage tank or recharge structure. Charcoal provides additional filtration.

[edit] Who can harvest rainwater? And where?

  • People planning house construction, house modification, existing house etc - from rooftops
  • Government buildings, institutions, hospitals, hotels, shopping malls etc. - from rooftops and open areas
  • Farmlands, public parks, playground, etc.
  • Paved and unpaved areas of a layout / city / town / village

There are few instances of serious illness linked to rainwater supplies, making it an effective source of water supply for many household purposes. Though there may be occasional bird droppings, these too do not represent a major health risk. However, placing taps at least 10 cm above the base of the rain water storage tanks allows any debris entering the tank to settle on the bottom, where it will not affect the quality of the stored water, provided it remains undisturbed.

[edit] Rainwater catchment systems

Rainwater catchment systems typically consist of three main components:

  • the capture system (roof and gutters)
  • the storage system (barrels or tanks), and
  • the delivery system (pipes, pumps, and valves).

Systems used in Sri Lanka involve placing a pot under a piece of cloth or plastic sheet tied at its corners to four poles. There is a hole in the center of the cloth which diverts the water to the pot after collecting it. In Germany, sophisticated computer managed systems are in use along with submersible pumps linking into the grey water and mains domestic plumbing systems. In between these two extremes are systems which are used in most domestic rain water harvesting. They mostly comprise a collection surface (a clean roof or ground area), a storage tank, and guttering to transport the water from the roof to the storage tank.

The maximum amount of capital investment is required for the water storage tank

Rain chains used in Japan are attractive ways of catching water from the roof for household purposes and gardening. The roof top of a house or a clean area in the ground is used as catchment area. Options for storing water are:

  • Plastic bowls and buckets
  • Jerry cans
  • Clay or ceramic jars
  • Cement jars
  • Old oil drums
  • Empty food containers

[edit] Storage of rain water

The storage of rain water on surface is a traditional technique and structures used are underground tanks, ponds, check dams, weirs etc. Recharge to ground water is a new concept of rain water harvesting and the structures generally used are:

  • Pits - Recharge pits, constructed 1 to 2 m wide and up to 3 m deep, are made for recharging the shallow aquifer. The pits are back filled with boulders, gravels, coarse sand.
  • Trenches - The trenches are normally 0.5 to 1 m. wide, 1 to 1.5m. deep and 10 to 20 m. long. They are made according to the availability of water and are filled with filter materials.
  • Dug wells - For possible use as recharge structure. Before water is put into dug well, it should pass through filter media.
  • Hand pumps - In case of limited water availability, hand pumps may be used for recharging the shallow/deep aquifers. Water should pass through filter media before being diverted into hand pumps.
  • Recharge wells - Constructed for recharging the deeper aquifers, the recharge wells are of 100 to 300 mm. Water is passed through filter media so that there is no choking of the wells.
  • Recharge Shafts - Recharge shafts of 0.5 to 3 m. diameter and 10 to 15 m. deep are constructed and used for recharging the shallow aquifer located below clayey surface. The shafts are back filled with boulders, gravels and coarse sand.
  • Lateral shafts with bore wells - For recharging the upper as well as deeper aquifers. The lateral shafts are 1.5 to 2 m. wide and 10 to 30 m. long. They are constructed with one or two bore wells and are back filled with boulders, gravels and coarse sand.
  • Spreading techniques – This technique is used when permeable strata starts from the top. Spread the water in streams by making check dams, cement plugs, gabion structures or a percolation pond.

[edit] Rainwater barrels

  • Watersaver Rain Barrels are 54-gallon units, made from quality durable black plastic a quarter of an inch thick and weighing only twenty pounds. It resembles a wine keg from medieval times with a cool look to it.
  • Deluxe English Barrels hold 77 gallons of water and is made from an attractive green plastic with an old fashioned English whiskey barrel design showing professionalism in its manufacturing. It comes with a four-foot hose, a drain valve for multiple rain barrel link ups, a debris screen and a tight childproof lid.
  • Rain Catcher Water Barrels are 54 gallon capacity fresh water receptacles, designed to fit in a compact fasion against the wall of your deck, patio or house, in a fine green that blends in well with your lawn or garden. This water barrel is child-safe and comes with a snug filter and lid, as well as overflow tube and linking kit for additional barrels in your rainwater catchment system.
  • Great American Rain Barrels are 60 gallon units, made from recycled food grade barrels three sixteenths of an inch thick. Rigid plastic like this can take anywhere from 200 to 500 years to find the way back to Mother Nature in the landfill, but when in use as a rain barrel, with a threaded spigot for easy hose attachment, screw-on-cover, drain plug, overflow fittings and complete instructions, it becomes a lifetime commitment to sustainable practices.

[edit] Tips for using harvested rainwater

  • Rain water harvested from roofs need to be analysed properly before use as they can contain animal and bird faeces, mosses and lichens, windblown dust, particulates from urban pollution, inorganic ions from the sea (Ca, Mg, Na, K, CL, S04) and dissolved gases including C02, Nitrogen oxides and sulpher oxides. For this reason in Gansu province harvested rainwater is boiled in parabolic solar cookers before being used for drinking. In Brazil water is disinfected with alum and chlorine before consumption.
  • In urban areas harvested rainwater can be used for flushing toilets and washing laundry.
  • In hard water areas it can also be used for showering or bathing.
  • Although it is not advisable to use rain water for drinking without treatment, in many parts of the world it is being treated to drinking also.

[edit] Rainwater harvesting around the world

Rainwater harvesting is followed in many parts of the world, such as Britain, China, Brazil, Thailand, Sri Lanka, Germany, Australia and India where rain and conventional water resources are in short supply because of overuse by a large population. Traditionally, people in arid and semi-arid areas harvested rainwater for drinking water, domestic water, water for livestock and water for small irrigation.

Gansu province in China and semi arid North East Brazil have the largest rooftop rainwater harvesting projects ongoing. In fact China has been successful in growing crops in a hostile terrain by developing low cost poly-house models with rain water harvesting and drip irrigation. These houses are made of mud with bamboo roofs covered with steel and plastic sheets using a mud wall, mostly bamboo structural roofs coupled with steel and plastic sheets for the roof. Due to acute scarcity of water in such regions rainwater is collected on the roof and brought inside the poly-house where it is stored in an underground cellar. It is possible to apply this technology in other areas of the world where there is shortage of irrigation water.

There is a residence in Toronto, Canada, that uses (treated) harvested rainwater for drinking, and reuses water (i.e. treated wastewater) for all other household water applications including toilet flushing, bathing, showers, laundry, and garden irrigation (Toronto Healthy House).

In New Zealand, many houses in smaller towns routinely rely on rainwater collected from roofs as the only source of water for all household activities. This is also the case for the very many holiday homes that exist.

[edit] Disadvantages of rainwater harvesting

  • Per capita cost is higher for a rain water harvesting system than for a communal pump or well.
  • The main disadvantage of rain water harvesting is due to the limited supply and uncertainty of rainfall.
  • As rainfall is usually unevenly distributed throughout the year, rainwater collection methods can serve as only supplementary sources of household water.

[edit] FAQs on rainwater harvesting

  • Do I need pumps to harvest rainwater?

If your barrel or tank is elevated just a few feet above the ground and your yard is small then you may not need a pump. You will require one if your tank is at ground level and you need to move the water up any slope

  • How big a yard can I water?

If you can capture a large amount of rain and have barrels placed all over your garden, then you can water a large area. It actually depends on you.

  • How big are rain barrels?

Rain barrels vary in size from a few gallons/liters to about 100 gallons (i.e. 378 liters). Most barrels are around 50-60 gallons (i.e. 189 - 227 liters). Rainwater tanks run from several hundred gallons/liters to many thousand gallons (i.e. 7,000 – 75,000 liters).

  • How do I raise the water pressure when I need to?

You can increase pressure by raising your barrel or tanks or by installing a pump.

  • Can I water my grass with rainwater?

You can but you will need very large tanks to hold water, as grass usually requires plenty of water.

  • Is water quality a problem in rainwater systems?

Rainwater generally doesn’t contain harmful minerals or chemicals. But today they are adversely affected by pollution. They can also be contaminated by animals in the catchment area. For this reason rainwater for drinking should be carefully stored and treated prior to consumption.

[edit] Water requirements and usage by a family (in India)

Liters per day per person

  • Drinking 3
  • Cooking 4
  • Bathing 20
  • Flushing 40
  • Washing clothes 25
  • Washing utensils 20
  • Gardening 23

Total 135

[edit] Rainwater harvesting and the environment

  • For self-sufficiency in water supply
  • Ground water pumping cost can be reduced
  • Opportunity to avail water of superior quality which are soft and low in minerals
  • When recharged to ground water, quality of water improves through dilution
  • Keeps soil erosion in check in urban areas
  • Less expensive
  • Simple system and can be adopted by individuals
  • Rooftop rain water harvesting can be constructed, operated and maintained with ease.
  • Preferred in hilly terrains
  • In saline or coastal areas, water quality improves on recharging to ground water. Salinity is improved and balance between the fresh-saline water interface is maintained.
  • Rain water harvesting is the most preferred source of water for domestic use in islands
  • Provides enormous relief to people in the deserts where rain fall is low

[edit] Unlearn

A well is not a storage tank to hold water. It helps to collect the rain water and charge it underground and later bring it out.

[edit] View it!

  • You Tube video on Urban Rainwater Catchment
  • Bringing Home Rain
  • Rain Chains used for hundreds of years in Japan.

[edit] References

  • Rainwater Harvesting: Technical Information Online
  • Deccan Herald Archives
  • Rainwater Harvesting:Frequently Asked Questions
  • Rain Water Harvesting and Artificial Recharge To Ground Water
  • Components of a Rainwaer Harvesting System
  • Rainwater Harvesting Guide
  • Methods of Rain Water Harvesting
  • Rainwater solutions Inc
  • Roof Top Rain Water Harvesting

[edit] Additional information

  • Manual for maintenance of rainwater in schools
  • Rain Water Harvesting

[edit] See Also