Rainwater harvesting

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This article describes the types of common rainwater harvesters which are usable in practice and which can be built DIY. [1]Also, it provides some basic how-to content on how the harvesters can be built in practice. Rainwater harvesters are devices used to gather, or accumulate and store rainwater. [2]

Contents

[edit] Systems

There are many types of systems to harvest rainwater. Notable systems are systems for runoff rainwater (e.g. hillside run-off) and rooftop rainwater harvesting systems. The type used depends greatly on the purpose (domestic or industrial use) and to some extent also on economics and physical and human considerations. Generally speaking, rooftop rainwater systems are most used as they are most economical (if there is more than 254mm of precipitation a year)[3] To determine the amount of precipitation falling in your area, refer to this map.

[edit] Domestic rooftop rainwater systems

[edit] System types

At the moment, 2 types of systems are generally used. These include DIY and commercial systems. Both of these systems are known under the term water harvesters and require only a limited amount of knowledge to set up (if basic systems are used). In both cases, the system consists of a storage tank to store the water and piping (to guide the water in). Additionally, extra pressuring equipment as pressure vessels, inline pump controllers or pressure sensitive pumps may also be required. [4] Finally, water purifying equipment as water-purifying plants, UV-lights or distillation equipment are sometimes (depending on local conditions [5] ) added to purify the collected water. The system is then called a Greywater treatment system. Greywater systems are usually preferred over regular water harvesters as they allow the system to not only treat the rainwater, but water from other sources as well (e.g. the watercloset; if plants are used). However, this feature may also be averted by using a UV-lamp and composting toilet instead.

Depending on local circumstances, a gravity-fed system may already be enough to have a pressured water collection system. [6] In the latter case, no pumps/pressure vessels are thus required to have a pressured system. In practice, gravity-controlled systems are usually created by placing the water harvester on an elevation (e.g. rooftops).

[edit] DIY domestic systems

As water conservation is becoming more and more popular, more people have begun to make their own homebrew installation. These systems range from traditional technologies like rain barrels to more complex greywater systems. Through the Internet, plans and accurate construction information have become available. [7] [8] [9] Depending on the degree of personal skill and preference, a more basic (regular water tank and piping[10]) -or more advanced (e.g. pressured systems with water treatment, etc.) system is chosen.

[edit] Commercial domestic systems

Commercial systems are also made. They are offered by a variety of companies ... Commercial rain harvesters can be obtained in both pressurized [11] as gravity-fed systems [12]. Greywater treatment systems are sold by companies as Nubian Water Systems, ... [13] Again, they are available in pressurised as gravity-fed systems.[14] [15]

[edit] System's operation

A mechanism can be used to send the initial water flow to waste, usually the first few liters. These are commonly known as 'first-flush' diverters, and are used to increase the chance that the large-particle residue that might accumulate on your collection surface is washed away from (and not into) your storage tank. Such a system also compensates for the fact that the initial minutes of a rainfall can include airborne pollutants being washed from the sky[verification needed], and likewise minimizes contamination of your captured supply. Simple but regular inspection and maintenance of such a device is usually necessary.

Not all catchment systems use such a feature. For example, rainwater in rural areas of Australia is traditionally used without such a system, and without treatment,[verification needed] but this may be unwise in different environments.

[edit] Practical use in autonomous houses/neighbourhoods

Most desert and temperate climates get at least 250 mm of rain per year. This means that a typical one-story house with a greywater system can supply its year-round water needs from its roof alone. In the driest areas, it might require a cistern of 30m³. Many areas average 13 mm of rain per week, and these can use a cistern as small as 10m³.

In many areas, it is difficult to keep a roof clean enough for drinking.[16] To reduce dirt and bad tastes, systems use a metal collecting-roof and a "roof cleaner" tank that diverts the first 40 liters. Cistern water is usually chlorinated, though reverse osmosis systems provide even better quality drinking water.

Modern cisterns are usually large plastic tanks. Gravity tanks on short towers are reliable, so pump repairs are less urgent. The least expensive bulk cistern is a fenced pond or pool at ground level.

Reducing autonomy reduces the size and expense of cisterns. Many autonomous homes can reduce water use below 10 US gal per person per day, so that in a drought a month of water can be delivered inexpensively via truck. Self-delivery is often possible by installing fabric water tanks that fit the bed of a pick-up truck.

It can be convenient to use the cistern as a heat sink or trap for a heat pump or air conditioning system; however this can make cold drinking water warm, and in drier years may decrease the efficiency of the HVAC system.

[edit] Industrial systems

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 US, rooftop rainwater is collected and stored in sump.[17] In India this includes Bawdis and johads, or ponds which collect the run-off from small streams in wide area.[18][19]

In India, reservoirs called tankas were used to store water; typically they were shallow with mud walls. Ancient tankas still exist in some places.[20]

[edit] References

[edit] External links