The Hardhof groundwater treatment plant was recently improved to provide additional capacity. This plant is one component of the Zurich system which serves not only the city but also over 57 municipalities. The improved facility incorporates three recharge basins that retain an average of 80,000 cubic meters per day with which to artificially recharge the groundwater supply. The water to recharge the groundwater supply is collected in 19 vertical wells located on the bank of the Limmat River. From four horizontal groundwater wells, a maximum of 150,000 cubic meters per day is conveyed to a pumping station that serves the plant's distribution zone. Buffer areas were established to prevent contamination of the water supply. Also, green space and sports facilities on the Hardhof site help to protect the drinking water supply. Includes tables, figures.