Water tanks are devices storing harvested rain from roofs. Rainwater tanks are installed to make use of rain water for later use, reduce on ones reliance for mains water use both for economic and environmental reasons but especially to aid self-sufficiency.
Rain is really distilled water precipitating after condensing at high altitude where temperatures are low. It matters not whether water falling from the sky is rain, hail, sleet or snow, it is all water and may be harvested.
The following is a guide to rain water tanks and rainwater harvesting in South Africa.
Stored rain water may be used for watering gardens, agriculture, flushing toilets, for washing machines, both laundry and dishwashing, washing cars, and also for drinking, especially when other water supplies are unavailable, expensive, or of poor quality, and that adequate care is taken that the water is not contaminated or the water is adequately filtered.
Submerged ground rainwater tanks may also be used for retention of storm-water (water from roof and paved areas) for release at a later time, though this is not suitable for use in the home. Conventional rain water ranks are not designed simply to put underground and backfilled with soil. These will collapse and may pop out of the ground if empty. Special underground tanks are built, but are very expensive otherwise a special room may be built with a concrete floor and roof with brick walls, all of which possibly make underground tanks unviable, but if this is the only source of water may this be necessary.
Water tanks may have a high (perceived) initial cost. However, many homes use small scale rainwater tanks to harvest relatively small quantities of water for landscaping/gardening applications rather than as a potable (drinkable) water surrogate. While all need to be to screen out mosquitoes, the lack of proper filtering or closed loop systems will create breeding grounds for mosquito larvae. An example of the screening process I with the Water Rhapsody Rain Runner, which filters harvested rainwater near the gutter, and this water may then enter an underground pipe to reach a remote rainwater tank.
If water is used for drinking, it should be filtered first. Filtration (such as reverse osmosis or ultra-filtration) will remove all pathogens. (Reverse osmosis is energy hungry and for rainwater this method of filtration should never be required.) Other filtration consists of ozone and UV (ultra violet) treatment. Reports of illness associated with rainwater tanks are very infrequent, and public health studies anywhere have not identified a correlation. Rainwater is generally considered fit to drink if it smells, tastes and looks fine.
Certain paints and roofing materials may cause contamination. In particular, lead-based paints should never be used even as a primer onto metal surfaces. Tar-based coatings may affect the taste of the water. Chemically treated timbers and lead flashing should be excluded from roof catchments.
Maintenance of rainwater catchment areas includes regular removal of vegetation and debris from rain gutters. So long as a rainwater tank is kept closed to preclude light from entering, no algae will grow, so the only maintenance that needs to be done is perhaps removal of the sediment on the floor of the tank once a year.
Water tanks may be constructed from materials such as plastic (polyethylene), concrete, plastered brickwork, galvanized steel, as well as fibreglass and stainless steel which are rust and chemical-resistant. By far the most popular and cost effective rainwater ranks are the plastic polyethylene tanks which are freely available from several manufacturers. It is imperative that the tanks are opaque to prevent the exposure of stored water to sunlight, to eliminate the possibility of algal growth.
Another imperative is that rainwater tanks should have a pre-filter under the eaves like the Water Rhapsody Rain Runner to prevent debris from entering the water tank/s and also to prevent any possibility of the feed pipe from a downpipe leading to the water tank (the ring main) from blocking. This pre-filter also prevents the ingress of mosquitos.
Apart from rooftops, tanks may also be set up to collect rainwater from concrete patios, driveways and other impervious surfaces. This water though may only be used for irrigation and toilet flushing, as it may be soiled from pedestrian and other animal use.
Initial sizes typically ranged in capacity from around 200 to 10,000 litres, or multiples of these. The most popular sizes are 2500 litres and 5000 litres, which are easily handled and are not unsightly.
Smaller tanks, such as the plastic 200-liter rainwater tanks are also used in some cases. These smaller tanks are mainly used in conjunction with a Garden Rhapsody Grey Water Re-using System. With this arrangement water tanks fitted above ground may flow by gravity into the Garden Rhapsody which has a pump incorporated into it and will pump the rain / grey water onto the garden. This can even be done automatically by trickle feeding the water from the higher rain tank/s into the Garden Rhapsody at all times, so that rain water flowing into the rain tank/s will not fill a tank that is full already, no matter how small the tank is.
Larger tanks are commonly used where there is no access to a municipal water supply. In this instance at no extra charge, Water Rhapsody will recommend a tank at a house taking into consideration a whole host of factors like: roof type surface (tile or metal), roof area in square metres, number of people drawing water from the rainwater tank, whether or not one has the rest of the Water Rhapsody systems in place to reduce ones consumption, and whether the house is a home, holiday home or a commercial or industrial building. To give an example of this calculation, (this was done by actuaries for Water Rhapsody): a typical metal roof will deliver 1000 litres of water from 100 square metres of roof for every 11 mm of rain. To get the same volume of water from a tiled roof one would need 16 mm of rain. Each middle class person uses 240 litres of water daily, so the draw from the rain tanks is very substantial. If one should install only two of the Water Rhapsody Systems to say: re-use grey water and the Water Rhapsody Multi-Flush to minimize toilet flushing, one reduces the demand for water to at worst half (of the 240 litres to 120 litres per person per day), but mostly down to as little as to 80 to 100 litres per person per day. Stored Rainwater then goes so much further without a change in lifestyle. The value of this calculation ensures that there is enough storage so that rainwater tanks need never overflow, and that one does not overspend on too many rainwater tanks that never fill.
All our water supplies will dry up very soon, which makes rainwater harvesting essential. A strategy microcosm of rainwater harvesting has been used by Jeremy Westgarth –Taylor of Water Rhapsody for the area of Knysna. This area has no storage dam, and relies totally on the water flowing from a river weir. The supply of water from the weir can no longer meet demand. Jeremy’s strategy would be to force everyone to install rainwater tanks to harvest rainwater from roofs, ban outright any irrigation from any other source other than grey water, and minimize toilet flushing water. Because the area is mostly a holiday destination, the volume of stored water together with the reduction of water demand would mean that the town of Knysna would create a large dam of many individual tanks. The total volume of stored water could be as much as 70 million litres. This would mean that the need for municipal water would be needed for two or three weeks per year, at the end of each holiday season, if at all.
The strategy formula for Knysna is a microcosm of what is imperative for implementation country wide.
The following is the typical use of water from rainwater storage tanks.
Most areas have seasonal rainfall. Very few have rain all year round. Water Rhapsody has devised a system whereby water stored in rainwater tanks is use during the rain season. This applies to areas supplied with municipal water but not able to meet demand.
Amortization of the cost of installation of water tanks. Amortization (paying off the capital) of rainwater tanks with the Water Rhapsody Grand Opus is best done by filling and emptying the rainwater tank/s as often as possible. As many times as any rainwater tank/s can possibly fill from rainwater from roofs, these should be drawn down to empty to avoid them overflowing next time rain should fall. Overflowing tanks mean that there is not enough rainwater storage in place or not enough people to consume water in the house. Rainwater tanks that never fill mean that too much storage has been put into place, or that there are too many people drawing from this water.
Water outages and emergency supply. Water Rhapsody has implemented a novel approach of an emergency supply if all rain water should be exhausted. This is coupled with an emergency supply when the municipality implement water outages as a means of demand management when demand exceeds supply. This system included in the Water Rhapsody Grand Opus is a means of keeping a days supply at all times when the municipality literally switches off the water. The system is full proof to ensure that it is impossible your precious stored rainwater cannot flow out into the municipal system.
Electricity outages. Electricity outages are something that pervades our age. Water Rhapsody include in the Water Rhapsody Grand Opus an override manifold so that if the user has no UPS (uninterrupted Power Supply) water will still be able to be used from a municipal source, if this does not coincide with a water outage. By simply switching valves, one may revert to municipal water.
Water Pressures. Rainwater pumped from rainwater tanks into a house with the Water Rhapsody Grand Opus may not exceed the pressure allowed for hot water cylinders of whatever type one uses. It is for this reason that Water Rhapsody has included within the override box an adjustable pressure reducing valve to suit the needs of any hot water cylinder if one should revert to municipal water supply. Whilst the rain water is pumped into the house one is quite safe from over pressurization as the Water Rhapsody pump is set to the correct pressure too.
Without general implementation of rainwater harvesting all South African towns’ cities and villages will not be able to continue expanding QED.
Lightning. During lightning storms some nitrogen in very small quantities is dissolved into the rain. This quantity is far too small to do any harm.
Lichen. Lichen is a symbiotic relationship between a fungus and algae, and the one cannot live without the other. This tuft of very precious growth on a tiled roof is one of the best indicators of pollution. So long as lichen grows on a roof the water that falls on that roof is safe for household use. Beware if all the lichen dies. Many people think that this growth is unsightly and should be removed and the roof painted. This is not true and ill advised. Leave the lichen alone.

NEW DELHI/BEIJING: A fight breaks out as student Vikas Dagar jostles with dozens of men, women and children to fill buckets from a water tank truck that brings water twice a week to the village of Jharoda Kalan on the outskirts of New Delhi.

A report released by the Water Research Commission of South Africa found that South Africa has 4% less water than 20 years ago.

Rand Water is predicting that demand for water in South Africa will outstrip supply by 2025. It also believes that Gauteng is potentially facing a water shortage as early as 2013.

In Cape Town the scenario is not much better with a water shortage prediction by 2016

If South Africans continue with their wasteful water practices, there simply will not be enough water to meet the country’s future needs and, we may have to start paying even more for water!
South Africans can change the scenario by changing their behaviour towards water usage and becoming water wise and savvy about rainwater harvesting.

Water Rhapsody can provide rain harvesting solutions as simple as a water tank and a filter, to our full blown Grand Opus system that also pumps rain water back into the home and only uses municipal water when the rain tanks are empty.