We have recently started using our Berkey water purifier. Our model is called the Berkey Light. It's made of thick blue BPA-free polyester. The Berkey claims to filter out all contaminants and pollutants to provide pure drinking water. There are other models that range from large stainless steel to handy sport size versions. In theory it can filter stagnant pond water into safe drinkable water. It is a simple and flexible natural method without the use of chemicals or a complicated process, especially helpful in situations where electricity and pressure are not available. It's a bit like a huge Brita filter. The unfiltered water is poured into the top container and it drips through two carbon filters into the lower container.