Water can be harvested in different stages of this cycle. Three typical ways of water harvesting are the collection of rainwater, harvesting water from surface waterbodies or obtain groundwater through wells or at sources.

In general, rainwater can be harvested from any run-off areas such as roofs, rocks and other surfaces. Depending on the amound of precipitation it is stored in cisterns, tanks, or large dams. The quality of the water and, hence, the possible application depends very much on the run-off area, the catchment system, and the storing. Rainwater can for example be harvested with appropriate installation from roofs. Generally, rainwater is of good quality, but lacks of taste, caused by the absece of minerals.

Rainwater can also be harvested as surface run-off and used for irrigation. In a broadbed-and-furrow system for example, runoff water is diverted into field furrows. The field furrows are blocked at the lower end. When one furrow is full, the water backs up into the head furrow and flows into the next field furrow. Between the field furrows are broad beds, where crops are grown. With this or similar systems, water is allowed to sink into the soil in order to raise the water-table and increase the soil-moisture leve. Generally, more water can seep into the soil if it is spread over a large area of soil rather than being concentrated into fast-running streams.

Through the contact with the roof, the cachment installations or by storing it in an imporper tank, rainwater can be contaminated with pathogens and has to be disinfected before drinking. Since every run-off area and storage facility burries the risk of contamination, water should be disinfected before using it as drinking water, for example by using the SODIS method (click to follow link). If no purification methods can be applied, only carefully collected and stored, clean rainwater, for example form a roof catchment (excluding thatched roofs), should be used for consumption. Water from natural pools should not be used as drinking water without purification and disinfection.

A rainwater harvesting system consists of three basic elements: a collection area, a conveyance system, and storage facilities. The collection area in most cases is the roof of a house or a building. The effective roof area and the material used in constructing the roof influence the efficiency of collection and the water quality. Roofs that could potentially leach toxins and pollutants should not be used for water harvesting. Galvanized, corrugated-iron sheets and tiles generally make good roof catchment surfaces. Flat cement or felt-covered roofs can also be used provided they are clean. Thatched roofs can make good catchments when certain palms are tightly thatched, e.g. coconut and anahaw palms. Most palms and almost all grasses, however, do not produce thatch suitable for high-quality rainwater collection, since they discolour the water and make it less palatable and attractive for domestic purposes. Although painted roofs can be used for rainwater collection, it is important the paint is non-toxic. Painted roofs must be kept in good condition so that the pain does not flock off into the tank. Unpainted and uncoated roof surfaces are best. Mud roofs are generally not suitable. Lead flashing and pesticide treated wood should also not come into contact with any rain water collected.

A conveyance system usually consists of gutters or pipes that deliver rainwater falling on the rooftop to cisterns or other storage vessels. Also drainpipes should be constructed of chemically inert materials such as wood, aluminium, or fibreglass, in order to avoid adverse effects on water quality. If PVC is used for the conveyance system, it should be protected from direct sunlight. The conveyance channel must be big enough to carry the water collected during high intensity storms, and the installation must be a sloped toward the storage tank at a minimum of .5 percent to ensure water flow and prevent blockages. To ensure that all runoff for the roof enters the gutter, splash-guards can be fixed to the roof. They normally consist of a lont strip of sheet metal, bent at an angle and hung over the edge of the roof. To prevents leaves, insects, and other debris from entering the storing tank, a stainless steel or copper-nickel mesh angled 60 degrees from the horizontal can be installed. Another mesh screen of 5mm, in an angle not less than 60 degrees from the horizontal should be installed about 3 cm above the tank inlet to screen the tank inlet. It should be at least 10 times larger than the cross-sectional area of the conveyance channel.

The water ultimately is stored in a storage tank or cistern, which should also be constructed of an inert material. Reinforced concrete, fibreglass, or stainless steel are suitable materials. Storage tanks may be constructed as part of the building, or may be built as a separate unit located some distance away from the building.

The first thing to do is to formulate the size of the reservoir. All rainwater tank designs should include as a minimum requirement: a functional and watertight design; a solid, secure cover to keep out insects, dirt and sunshine; a screened inlet filter, a screened overflow pipe, positioned at the maximum water level of the tank; access for cleaning, like a manhole, an extraction system that does not contaminate the water, e.g. tap/pump: a soakway to prevent spilt water forming puddles near the tank; a maximum height of 2m to prevent high water pressures (unless additional reinforcement is used in the walls and foundations). Additional features might include: a device to indicate the amount of water in the tank; a sediment trap, tipping bucket, or other "foul flush" mechanism; a lock on the tap; a second sub-surface tank to provide water for livestock, etc. To prevent dust, sediment and other debris on the tank floor from entering the draw-off pipe, the tap should be elevated 5cm above the floor. Although this arrangement creates a "dead storage" of 5cm at the bottom of the water tank, it has three benefits: it prevents sludge on the tank floor from reaching the outlet tap, thereby protecting water quality. It ensures water is retained even in an otherwise empty tank, keeping the tank interior moist and protecting the tank from cracking in hot weather.

All catchment surfaces must be made of non-toxic material. Painted surfaces should be avoided if possible, or, if the use of paint is unavoidable, only non-toxic paint should be used (e.g., no lead-, chromium-, or zinc-based paints). Overhanging vegetation should also be avoided.

This technology is useful for people cannot afford a metal roof and are not near other sources of free water like springs, wells or boreholes, but who have trees in their compounds. Rain falling on the foliage runs down the tree trunk, and is funnelled by a banana leaf or metal sheet attached to the trunk into a bucket, pot or storage tank. Rainwater can be harvested from trees anywhere: it is a question of finding out which trees are appropriate. The best ones have short, smooth trunks, thick crowns and heavy foliage. Jackfruit (Artocarpus heterophyllus) and wild fig (Ficus natalensis) are very suitable. This method is cheap and easy to set up. While the water collected is not as clean as that from a metal roof, it is cleaner than that collected from thatched roofs. It should be filtered and boiled or SODIS should be applied if it is used for drinking.

Contaminants from a roof are usually concentrated in the first run off from the roof. After this runoff has passed and washed the roof the water is considerably safer. The amount to be removed varies and a number of studies have had differing results. Despite this uncertainty, first flush systems are a popular method of improving the quality of roof runoff prior to storage, particularly in Asian countries. The two commonest systems use either a floating ball or a tipping gutter to divert and/or store the first flush away from the storage tank.

The tipping gutter first flush system is very simple to build, operate, and maintain. Water from the roof lands on a piece of guttering which is tipped down away from the water tank. Therefore the first rains and their debris pour away from the tank and into a storage vessel. The end of the guttering is attached via a pulley to the diverted water tank, and so as the diverted water tank gets fuller (and therefore heavier) it lifts up the end of the tipping gutter. Now the (hopefully) clean water from the roof is directed into the water tank.
The diverted water tank has a small bore pipe fitted near its bottom out of which the accumulated diverted water can escape. Over time the dirty water will leak out and the tipping gutter will reset ready for the next rain shower. Obviously if it is still raining by the time the diverted water tank has emptied, some water will be lost as the diverted water tank will have to be filled up again (this time with clean rainwater) before water is again allowed into the water tank.
A small amount of wastage is more than made up for by the simplicity and elegance of this first flush system. However, if water really is in very short supply then a tap can be fitted to the diverted water tank so that the dirty water can be released manually when the rain has stopped. This saves waste, however if the system is to be left for a few weeks unattended, contaminated water would get into the main clean water storage tank if it rained.

The floating ball first flush system is a little more complicated than the tipping gutter system discussed above although they have some similarities. When the rain starts to fall it accumulates together with any debris in a chamber with a conical top. As the chamber fills a ball floats on the collected water's surface. Eventually the ball becomes stuck in the conical chamber entrance blocking the bottom chamber and therefore redirecting subsequent collected rainwater into the main clean water storage tank.
As with the tipping gutter system, a small bore pipe is used to slowly drain the water from the lower chamber to automatically reset the first flush device. Again a tap can be used if water is at a premium since water dribbles out continuously when it is raining.

Every roof and every location is different. Basically, the larger the roof and the longer the periods between rain fall, the larger the quantity of water which must be disposed of in the first flush. In the case of the tipping gutter system this is achieved by using a suitably large diverted water tank and weighting the gutter to ensure that it tips when the required amount of water has been diverted. Again with the floating ball system, the bottom chamber of the first flush tank must be sized appropriately so that rainwater is only allowed into the storage tank after the first flush has been collected.

Water from surface water bodies has to be disinfected if used as drinking water, e.g. by using the SODIS method (click to follow link).

Also above the water table, the soil can hold some water, but the pores are not completely filled with water but also with air. Water in this soil layer is called soil moisture.

There can be multiple aquifers at the same site (see illustration). In the illustration, two aquifers are shown. The upper, unconfined aquifer is not protected by an impermable layer above; the upper border is constituted by the water table. In this case, water can directly infiltrate from the surface and can contaminate the aquifer, e.g. if water from a latrine drains into the aquifer. The lower aquifer has a protecting, impermeable layer above it, so no water can directly infiltrate from the surface. These aquifers are often called artesian aquifers. Wells can be dugged or driven into both kinds of aquifers. In an artesian aquifer, the piezometric surface is the level to which the water will rise within a well. If the opening of a well lies below the piezometric surface of the aquifer it is build into, the water flows continuously, driven by the force of the waterpressure.

The ground water can be seen as a natural water reservoir. The water is filtered by the ground and normally quiet clean, but it can still be contaminated, especially in aquifers that have no protecting layer above. Groundwater does not neccessarily be refilled by infiltrating or percolating rain water. Some aquifers have stored water for a long time and do not get refilled. Such aquifers have to be used wisely. To use the ground water for household or farm use, it has to be transported up to the surface, either by a pump or by manpower. Where the water table meets the surface, natural swamps, sources, or other open water bodies appear. Groundwater should be disinfected before used as drinking water.

Shallow wells are usually not more than 15m deep and do not penetrate harder rocky layers. They reach a groundwater layer that is only protected by a permeable soil layer. Quality and quantity of water can vary during the year, especially when dry and wet seasons are ocurring. Unprotected aquifers are easily contaminated by latrines, soakways or waste disposals and, hence, the location of a shallow well has to be choosen with care. Disinfection of the water is required in any case. Shallow wells are also called water table wells