Westfriese Omringdijk and PWN Andijk. PWN is the first company in the world to apply UV/H2O2 purification on a large scale. With this purification method, no chlorine or ozone is used. The Westfriese Omringdijk runs here to the right of the reservoirs..© 28 juni 2019 Aerophoto-Schiphol Aerial Photography