Icas is an infiltration area in the dunes of the Noordhollands Duinreservaat (North Holland Dune Reserve). This is an important area where the nature is used for purifying drinking water.

This dune area has a freshwater bubble under the dunes. Previously only natural dune water was pumped up from the bubble to make drinking water. As a result, the fresh dune water ran out and nature dried up. Nowadays, as much water is infiltrated into the soil as is pumped out.

The water in this infiltration area has already travelled for kilometres. It comes from the IJsselmeer and is first pre-purified. Through 50 kilometres long pipes, the water is pumped into the Icas-area through the water inlet point De Kwal (The Jellyfish), where 800 liters of water are pumped per second into infiltration channels.