Xai-Xai IDP – INFRASTRUCTURE PRELIMINARY PROJECTS
The supply well is situated in the middle of a built-up area some 30m from a newly renovated toilet block, which discharges via a septic tank into a soakaway. There is a risk of pollution and steps should be taken to monitor water quality and to minimise the pollution risk. This problem will get more severe as water consumption increases and also as a number of tourists increase and the toilet block becomes more heavily loaded.
Standby pumping is required in case of pump failure, as well as an auxiliary generator in case of power failure. During a storm at the end of July 1998 the power was interrupted for 16 hours and intermittently thereafter for shorter periods. The supply of water to the town was interrupted for almost two days over this period.
Delivery to reservoir must be checked against the meter to determine if 20m3/hour is really being delivered. The 75 mm dia pumping main is on the small side for such volumes which generate velocities in excess of 1,2m/second.
Storage is much too small for pumping rates of 20m3/hour representing only 2 hours storage at this rate (40m3). Moreover, projected water consumption can be expected to reach 400m3/day (see Annex I) within a year or two if rehabilitation of existing houses and development continues and if water is made available to the existing inland villages as required. Storage should be provided for 48 hours being standard practice for a pumped supply system, which equates to a minimum of 800m3 (not 40m3 as at present). In addition, the old reservoir is built with a top water level of only 60m which is too low to supply much of the adjacent area.
Reticulation was believed to be leaking badly and may have to be replaced in part or in its entirety. However, brief initial investigations on 21 September allowed the reticulation to be inspected at six points, two of which exhibited dampness with minor weeping of water (not serious) while one leak in the pavement next to the hotel was more serious. Pipes exposed were a mixture of asbestos cement, galvanised iron and uPVC.
The condition of the reticulation may, therefore, not be as bad as first thought and new connections should continue to be made to serve rehabilitated or new residences. No plans are available so the strength of the reticulation is uncertain. Therefore, the reticulation should be exposed on a systematic basis and proper plans prepared. This will enable the system to be checked for leaks and will enable the capacity of the system to the town to be calculated. In the past, when the big hotel was operating, it had large storage tanks and its own well so placed produced little load on the system. The hotel also had a large generator to provide standby power for its pumps.
Summary of Existing Systems
The present system is in a poor condition and is unable to provide an assured water supply to the town. The main problem is it has very little reservoir storage (only 5% of current requirements), it only has one pump dependent on an erratic electricity supply without standby pump or generator. Moreover the source of water is a well which risks pollution from nearby septic tanks or possible salt water contamination if over pumped (it is only 100m from the sea). Finally, the reticulation is old and uncertain and unlikely to be able to meet peak demands if major hotels are to be built. There is also a risk of local pollution through possible contamination on many occasions when the pipes stand empty when the pumps fail. The danger of pollution through the reticulation is also increased because there is no system of chlorinating to treat the water and protect against contamination and impurities.