Salt content of reclaimed water from sanitation facilities in informal settlements and management options for sustainable agricultural irrigation

For long-term sustainable irrigation of agricultural areas, salt accumulation on the fields needs to be controlled. In areas where rainfall is high at least during some time of the year, infiltrating water is usually sufficient to leach salts from the soil. In arid and semi-arid regions, rainfall might be too scarce, and additional measures for the removal of salts from the root zone are necessary. This paper presents data on water quantities, electrical conductivity (EC), and total dissolved solids (TDS) from a research project with agricultural water reuse in North Namibia and discusses options for salinity management. During planning, TDS were quantified using literature data. After implementation, quantities, EC, and TDS of tap water and reclaimed water were monitored. Mean water consumption is 61-64 L per capita equivalent and day. TDS loads are about 20-21 g/(capita equivalent x d) and thus lower than reported in literature. TDS loads in the water can be reduced by measures such as urine separation or reverse osmosis membrane filtration. However, accumulation on the field is still considerable in the long term. Salt uptake in crops is only substantial to the salt balance if TDS contents of the irrigation water are relatively low. Therefore, in the majority of cases, regular drainage and leaching of the fields are necessary. The per capita TDS loads and water quantities presented in this work are specific results collected from the facilities implemented in this project. They can serve as a basis for estimating water quantities and excreta loads for similarly managed sanitation facilities.