Regnvatteninsamling från hustak på södra Gotland / Rainwater collection from a roof on southern Gotland, Sweden

The availability of drinking water from water wells on southern Gotland is highly limited on account of the fractured limestone bedrock of the region, and one possibility for supplying water in this region is to collect rainwater from roofs. For several years, rainwater was collected from a roof on southern Gotland in order to supply a basic household with water for drinking, dishwashing, bathing, etc. After collection, the rainwater percolated through a sand filter before it was used by the household. The aim with this study was to investigate if the sand filter had been effective against microorganisms in the collected water, and if the water quality, in terms of microbiological criteria, had been improved by filtration. The analytical results show that the rainwater that was collected from the roof contained between 6.4 × 105 and 1.5 × 107 living microoganisms per milliliter water and contained E. coli, which suggests that the water had been in contact with feces, most likely bird droppings on the roof. The results from the microbiological analyses indicated that rainwater treatment with a finegrained sand filter delivered water that was suitable as drinking water, or suitable with limitations according to Swedish drinking water criteria. The results suggest that a better filter function can be attained by increasing the sand thickness and thus increasing water residence time in the filter.