Converting sewage holding tanks to rainwater harvesting tanks in Poland

The aim of this study was an assessment of feasibility of conversion of sewage holding (SH) tanks to rainwater harvesting (RWH) tanks in Poland. Such a conversion may partly solve the problem of water scarcity for irrigation of plants in individual small gardens and reduce tap water consumption. Seven methods of RWH tanks sizing were applied to an example of a small harvesting system of the roof area equal to the garden irrigation area of 100 m(2) for three different irrigation doses. A new criterion was introduced to optimize the tank capacity. Economic optimization was provided for new RWH tanks and for the tanks adapted from abandoned SH tanks. Results obtained for a system sited in west-central Poland in an average year have shown that design capacity of RWH tanks varied markedly between sizing methods. The conversion of SH tanks to RWH tanks is profitable, especially for irrigation due to scarcity of water in relatively dry west-central regions. Conversion of individual SH tanks in a good technical state to RWH tanks is relatively simple and cheap. The potential increase in storage volume due to the conversion of individual SH tanks to RWH tanks could reach all over Poland 215-350 dam(3) per year, and individually can save up to 18-25% of total annual water use.