i asked the question because i read somewhere that they ''polish'' the water, remove really tiny particulate matter and make the water almost disappear, due to its appearance, clarity etc...i had quite green water from howick beach which i got on the 18th. ive since collected 720lts on fri morning and done a 100% w/c. thanks to steve for use of his pump, it took 10 mins to load on board...brilliantly easy!!