thought the tanks were plastic peter a pinch of potassium permangante then or a spoonfull of thin bleech and there must be other water sterilisers on the market m8 im sure they could find something if there that concerned about the water a swallow flys 3000 mile with a drink from a puddle all wild birds drink dirty water and it does them no harm think we are looking for problems that are not there or excuses maybe ino its lack of water and bops we should be looking at peter