For capacity extension of one of the drinking water production plants of Amsterdam Water Supply, four treatment schemes applying ultrafiltration (UF) are considered. The main purposes of the UF process are phosphate removal, removal of suspended solids and colloidal matter; and hygienic water quality improved. In the pilot plant investigation, water from the Bethuynepolder has been treated with FU. The feed water shows very large and rapid water quality variations, making it a difficult source to treat with UF. Hydraulic performance as well as effluent water quality were studied. The results have shown that stable operation of the membranes is feasible and an excellent water quality can be produced. Phosphate was removed from average 60 μg/1P to 20 μg/1P in the utlrafiltrate. Iron and turbidity were almost completely removed, whereas a log-removal of at least 2.5 and 3.5 was reached for indicator organisms. It was concluded that UF is a powerful treatment process for extension of drinking water production at AWS and offers new opportunities for relatively small-scale, on-site production of household or industrial water.