Hydraulic ram pumps and Sling Pumps

Table1: Rainwater reservoirs at public buildings in Lobatse, BotswanaThe reason for not fixing a uniform tariff throughout all towns (W.U.C. supplies water in urban areasonly) is to keep people aware of the more or less permanent shortage of water with emphasis onareas where the supply becomes very expensive. As a result of growing urbanization (Botswana'surbanization rate in the past was 11.2% per year, one of the highest in the world) more and moreinvestment was necessary for well drilling, dam raising and pipeline construction. As shown in Table2 water tariffs have been increased each year since 1982. The tariff is stepped up and the tablecalculated on the amount of 50 m³ and more. The tariff for the first 10 m³ is much lower but was alsoraised from 2.30 pula in 1982 to 5.20 pula in 1987. That is equivalent to an increase of 126% withinjust five years. However, prices for water consumption of 20.50 m³ and more increased much more.As the table shows, 50 m³ in 1982 cost 30.10 pula; the 1987 cost is 80.10 pula. This means anincrease of 166% which is more than two and a half times the cost of five years ago. It could beargued that another tariff policy would be more justified. However, the system in use has definitelysupported water saving and the rainwater reservoirs at public buildings in Lobatse become moreand more economical. The costs of filling given in Table 1 are based on the sizes of the reservoirs,not on the consumption. It is unfortunately not possible to state an average amount of consumptionsince gardening is of different intensity and gardening areas vary. Refilling of all reservoirs is donethree times a year if there has been no rain. This suggests a consumption of about 1,300 m³equivalent to costs of 2,150 pula. This amount would still cover the construction Cost of a reinforcedbricktank capacity of 21 m³ As the example shows, this dual systems is economically efficient. At thesame time, the reservoirs are an ideal stand-by facility. Given the case that the centralized systemmay be temporarily not functioning, the cisterns could supply the population in the area of location.As all reservoirs are closed, a treatment with chlorine could make the water safe for use. Since itcan be observed everywhere that the highest consumption of water is in areas where drinking waterquality is not imperative, raw water should be used as much as possible.7