We have recently moved to a flat where the only water supply is borewell water. I find that my water bottles etc. start to turn greenish at the bottom if the water remains for a few days. This happens to the level indicator of my Aqua Sure storrage purifier also. I have never had this happen to my water purifier before. The storage unit however does not seem to be turning green although I only wash it every 10 days or so. Is this dangerous? Does it mean there is algae in the water? Do I need to install Aquaguard system? The water has a slightly hard waterish taste but is otherwise odour free and clear.