The researchers tested different ways to clean water at a plant in Amsterdam. They used a process called ultrafiltration to remove things like phosphate, dirt, and germs from the water. The results showed that the ultrafiltration process worked well and made the water very clean. They were able to reduce phosphate levels by a lot and remove almost all the dirt and germs. This means that ultrafiltration is a good way to make drinking water safer and can be used in small-scale water treatment for homes or businesses.