Maintenance

• Before collecting water the roof, gutters and tank should be cleaned
• Let the first 2-3 rains flow out through the first flush system
• Remember to clean the tank once in a year
• Replace the filtering agents every year
• Keep the tank and surroundings clean and hygienic
• Apply white cement on the tank every year
• Make sure that sunlight does not pass through the manhole to prevent algae growth
• Remember to preserve water and use it judiciously

Components

A Roof water harvesting system should have the following components:

Down pipe and first flush arrangement

This is an arrangement to prevent the dust and other unwanted materials that may be seen on the roof, from reaching the storage tank. By fitting a down pipe with an end cap or valve can ensure that the washed water from the roof does not reach the storage tank. It is always safe to ensure that the first flush arrangement remains open during non- rainy days and should be closed after first rain up to the satisfaction of the end user.

Filter unit

The rainwater collected from the roof should be allowed to reach the storage tank only through a filtering mechanism. Rubble, sand and charcoal, as used in the traditional three-pot filtration, can be adopted here. 10 cm thick 20mm rubbles, 10 cm thick charcoal/coconut shell, 15 cm thick coarse sand, 5 cm thick 6mm rubbles etc. may be arranged from bottom to top in the filter unit. The water that is passed through this filter should remain safe for a long period of storage. Charcoal/coconut shell is added to eliminate gaseous pollutants.

Storage tank

Mainly three types of storage tanks are constructed for roof water harvesting. They are aboveground, underground or sub surface tanks.

Provision for drawing water and spill over

For drawing water from the storage tanks any method may be adopted provided it shall be drawn only when needed. The easier the method adopted for drawing water, the more will be the chances for its misuse. Three types of drawing water are usually adopted. They are by using a tap (small capacity tanks with basement and over ground tanks), hand pump (under ground tanks) or electric pump sets (large capacity tanks).

It is important that the system is sized to meet the water demand throughout the dry season. In general, the size of the storage tank should be big enough to meet the daily water requirement throughout the dry season. In addition, the size of the catchment area or roof should be large enough to fill the tank.

Ancient period

Rainwater harvesting has been used since biblical times. It was done in ancient Palestine, Greece and Rome. Around 3rd Century BC., farming communities in Baluchistan and Kutch used it for irrigation.^[5]In Ancient Tamil Nadu, India, Rainwater harvesting were done by Chola kings.^[6]Rainwater from Brihadeeswarar Temple was collected in Sivaganga tank.^[7]In the Indus Valley Civilization, Elephanta Caves and Kanheri Caves in Mumbai rainwater harvesting alone has been used to supply in their water requirements.

Now

• Currently in China and Brazil, rooftop rainwater harvesting is being practiced for providing drinking water, domestic water, water for livestock, water for small irrigation and a way to replenish ground water levels. Gansu province in China and semi-arid north east Brazil have the largest rooftop rainwater harvesting projects ongoing.
• In Bermuda, the law requires all new construction to include rainwater harvesting adequate for the residents.
• The U.S. Virgin Islands have a similar law.
• In Senegal and Guinea-Bissau, the houses of the Diola-people are frequently equipped with homebrew rainwater harvesters made from local, organic materials.
• In the United Kingdom water butts are often found in domestic gardens to collect rainwater, which is then used to water the garden. However, the British government's Code For Sustainable Homes encourages fitting large underground tanks to new-build homes to collect rainwater for flushing toilets, washing clothes, watering the garden, and washing cars. This reduces by 50% the amount of mains water used by the home.
• In the Irrawaddy Delta of Myanmar, the groundwater is saline and communities rely on mud-lined rainwater ponds to meet their drinking water needs throughout the dry season. Some of these ponds are centuries old and are treated with great reverence and respect.
• Until 2009 in Colorado, water rights laws almost completely restricted rainwater harvesting; a property owner who captured rainwater was deemed to be stealing it from those who have rights to take water from the watershed. Now, residential well owners that meet certain criteria may obtain a permit to install a rooftop precipitation collection system (SB 09-080).^[8] Up to 10 large scale pilot studies may also be permitted (HB 09-1129).^[9] The main factor in persuading the Colorado Legislature to change the law was a 2007 study that found that in an average year, 97% of the precipitation that fell in Douglas County, in the southern suburbs of Denver, never reached a stream—it was used by plants or evaporated on the ground. In colorado you cannot even drill a water well unless you have at least 35 acres. In New Mexico, rainwater catchment is mandatory for new dwellings in Santa Fe.^[10]
• In Beijing, some housing societies are now adding rain water in their main water sources after proper treatment.

Professor Micheal McGinley established a project to design a rain water harvesting prototype in the Biosystems design Challenge Module in University College Dublin.

• In Australia rainwater harvesting is typically used to supplement the reticulated mains supply. In south east Queensland, households that harvested rainwater doubled each year from 2005 to 2008, reaching 40% penetration at that time (White, 2009 (PhD)).

In India

• In Tamil Nadu, India rainwater harvesting was made compulsory for every building to avoid ground water depletion. It proved excellent results within five years and every other state took it as role model. Since the implementation, Chennai saw 50 per cent rise in water level in five years and the water quality significantly improved.^{[11] [12]}
• In Rajasthan, India rainwater harvesting has traditionally been practiced by the people of the Thar Desert. There are many ancient water harvesting systems in Rajasthan, which have now been revived ^[13]
• Kerala, India,

As rainwater may be contaminated due to pollutants like microscopic germs etc., it is often not considered suitable for drinking without treatment. However, there are many examples of rainwater being used for all purposes — including drinking — following suitable treatment.

Rainwater harvested from roofs can contain human, animal and bird faeces, mosses and lichens, windblown dust, particulates from urban pollution, pesticides, and inorganic ions from the sea (Ca, Mg, Na, K, Cl, SO₄), and dissolved gases (CO₂, NO_x, SO_x). High levels of pesticide have been found in rainwater in Europe with the highest concentrations occurring in the first rain immediately after a dry spell;^[3] the concentration of these and other contaminants are reduced significantly by diverting the initial flow of water to waste as described above. The water may need to be analysed properly, and used in a way appropriate to its safety. In the Gansu province for example, harvested rainwater is boiled in parabolic solar cookers before being used for drinking.^[4] In Brazil alum and chlorine is added to disinfect water before consumption.^{[citation needed]} So-called "appropriate technology" methods, such as solar water disinfection, provide low-cost disinfection options for treatment of stored rainwater for drinking.

Rainwater harvesting can ensure an independent water supply during water restrictions, though somewhat dependent on end-use and maintenance, usually of acceptable quality for household needs and renewable at acceptable volumes, despite forecasted climate change (CSIRO, 2003). It produces beneficial externalities by reducing peak storm water runoff and processing costs. In municipalities with combined sewer systems, reducing storm runoff is especially important, because excess runoff during heavy storms leads to the discharge of raw sewage from outfalls when treatment plant capacity cannot handle the combined flow. Rainwater harvesting systems are simple to install and operate. Running costs are negligible, and they provide water at the point of consumption. Rainwater harvesting in urban communities has been made possible by various companies. Their tanks provide an attractive yet effective solution to rainwater catchment.

Rain water harvesting law Some U.S. states have water law in favor of land owners, and some states own all water rights, leaving the owner only water rights the states are willing to grant through permits. For example, in Colorado you may not catch, collect or harvest rainwater from your roof unless you first buy a permit.

In Australia In Australia it is common to have a rain water tank with rainwater running off the house roof to fill tank, it is common to flush toilets with this water and have a back up valve like an Acquasaver that gives the home owner mains(town water) as a back up in case rainwater supply is exhausted or power failure. These types of valves automatically switch from rain water to mains water supply when available, so the homeowner never needs manually operate this valve.

In Sri Lanka Urban Development Authority of Sri Lanka has been directed to include rain water harvesting by changes to its act of establishment.

Rainwater may also be used for groundwater recharge, where the runoff on the ground is collected and allowed to be absorbed, adding to the groundwater. In the US, rooftop rainwater is collected and stored in sump.^[1]by 6 th std student