Description:
Looking at the costs and benefits, centralized systems may not be the answer in terms of best result for the investment. The chart on the left shows that the financial NPV does not change with increasing population size for centralized sewage and wastewater connection, however the economic NPV (which includes benefits to health and the environment) shows a positive trend with increas- ing populations. Centralized systems therefore generate a greater benefit as population increases, but show a significant loss with small community size. The chart on the right shows the situation where decentralized latrines have been installed, and where the excreta is reused for food production, and hence the overall benefits returned will depend on the current market price for food. With a good market, the reuse benefits of low-cost latrines can be realized by the households into a positive NPV, however those requiring greater investment, do not offer a return on the investment (WSP, 2006).