| Water Saving and Reuse of Water |
| Water Saving and Reuse of Water |
Water saving in semi-desert countries is essential and should be encouraged as much as possible. To support saving, it is first important to understand how water is wasted.
By way of example, let us consider a selfhelp housing area. In Botswana this area is supplied through standpipes on the side of streets, never more than 100 metres away from a house. Tenants are supposed to build pit latrines before they are allowed to construct dwelling rooms. People fill containers several times a day and carry the water home. Although the supply of water is much better than in villages and distances are much shorter, the water still has to be carried. One who has to carry water to the point of use will hardly waste it, and exactly this is the experience gained. It was observed that people became used to collecting their washing water after use, and watering their plants in the courtyard. As the water bills in Lobatse showed, consumption of water per standpipe in self-help housing areas, although used by 7-10 families, is lower than the consumption for one high cost house. It has been suggested that the consumption in residential houses rises with the number of taps and other sources connected to the central supply. Unfortunately, statistics are not available but observations appear to confirm this. However, the conclusion from the above should not be to propose public standpipes as a solution. The general conclusion can only be that the convenience of access to water raises consumption. If this is understood, we should have a close look at possibilities of saving domestic water.
In domestic water use the waterborne toilet system, in general, is the highest consumer of water. Moreover, the water used is not fit for reuse and goes into the sewers. Recycling of sewer water is possible but expensive and can only be done in special ponds. It has been observed that at a school with water closets (12 toilets each consuming 10 litres per flush), the consumption of these flush toilets is higher than the consumption of 1000 pupils and their teachers for drinking, cooking one meal a day and washing the dishes. Consumption reduction means first reducing the consumption by the toilets. Flushing valves consume less than flushing cisterns, but they are not appropriate since they require a permanent high water pressure not always available in developing countries. There are producers of toilets consuming 4 litres of water per flush in Sweden, Great Britain and West Germany. Imports of this highly appropriate system into developing countries, where there is a real need to save water, should be encouraged. In Botswana this was done by the Botswana Technology Centre in Gaborone. This institution had discussions with wholesalers whom they persuaded to import a reasonable number. At the same time the centre spread information about this new system. Introduction of a new system like this takes time since people have to be convinced that the higher investment really brings returns. But there is also something that can be done about the existing highly wasteful cisterns. Some can be adjusted to lower levels of filling by bending the bow of the cistern float downwards. This results in stopping the filling water at a lower level. It is also possible to put stones around the off-flow of the cistern. The volume of the stones (blocks) will be the volume of water saved, at the same time raising the water level to the adjusted cistern float. Depending on the type of cistern the consumption can be reduced to 7 or even 6 litres, but the cleaning effect of flushing is reduced since the toilet bowl is not designed for such low consumption.
It is often not realized that the amount of water consumed for one bath is sufficient for three showers. In consequence this would mean that houses should be furnished with showers rather than with baths. But baths have become a status symbol in many countries, and a high cost house must be furnished with a bath. The amazing thing is that baths in Europe are rather out of fashion and much less used than showers which produce savings in both water and time. From the hygiene point of view showers are better than baths. If a bath is installed this should always be done in such a way that a shower battery is fixed, so that the bath can also be used for showers. At the same time the built-in bath should be chosen carefully since the capacity varies substantially. Several devices are on the market designed to reduce water consumption. Spray nozzles for showers, push button taps etc. might reduce consumption, but should be studied before use. When deciding on water saving equipment one has also to consider the lime content of the water. Lime precipitates at 60 °C. This means that sensitive equipment in hot climates will soon clog.
Major sources of water consumption in residential houses are the kitchen sink, the bath and/or shower, the basin in the bathroom and the toilet. While for obvious reasons the reuse of water from the toilet is not possible, the bathroom water, although contaiminated by soap and through laundry by washing powder, can be used for cultivation, even for vegetables if directed at the soil. One vegetable gardening area of 150 m² at a clinic in Lobatse was irrigated with water from sinks and hand basins only for a period of one year, and showed very successful results. At this clinic only one sink was used for washing drug containers and equipment used for medical tests. This waste water was drained into the sewer. All other waste water was drained into drums dug into the ground (see Fig. 1.3). The water was then extracted with buckets and used for gardening. Experiments at private residential houses have shown that the reuse of water for gardening does not affect the plants, if the water is drained into the soil surface only. This does not generally apply to water running out of the kitchen sinks. Water from dishwashing usually contains too much grease and is therefore not suitable for most plants nor for vegetable gardening. But this water can be successfully used, for example, for cultivation of banana plants. Bananas should not be planted closer than 15 metres to a residential house because of mosquito breeding.
There are two ways to reuse domestic water. The first, as stated, is to disconnect the pipes of the sink outlets and fit hoses draining the water into drums dug into the ground.
These drums must be provided with lids because of the danger of mosquito breeding. Water is then lifted out with buckets. The other and more convenient method is to connect long hoses direct to the outlets and draw the water straight to the place of use.
Where rainwater is available and not used for the household and as drinking water because of an existing centralized supply, it should be used for vegetable gardening and the waste water for cultivation of trees and other plants (see Fig. 1.3). Vegetable gardening with waste water requires the cultivation of vegetables where only the above-ground part of the plant is eaten, and the water is spread on the soil. and not sprayed onto the leaves.
The water catchment possibility is always limited to the amount of rainfall, as is the storage capacity. Therefore, dependence on rainwater should always be seen in correlation with water conservation.
