That’s what we though as well, but interviews showed it was not really necessary for the user. Once the filter runs, they hardly ever have to maintain. Many of them also would not have the money for two filters. And everything is also a matter of comparison. Even if the user doesn’t wait for four weeks, the water quality is still much better than the raw water. Often it is also just enough to stir the sand a bit, which causes a faster flow rate again, but the water quality improves quickly. I know this is quite against the literature, but we found out the schmutzdecke is not as disturbed as you might think.
As to running 2 filters so as to allow a source of reliable water during maintenance of one of them, this might seem a right solution, but it is hardly appropriate in the context where we work and where even the cost of one filter constitutes already quite a drain on the income of each household. In any case, what we aim for is to find an appropriate, affordable solution that provides a huge improvement in the quality of drinking water available to the poorest communities in Africa – not a perfect solution that is safeguarded against all possible eventualities.
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