Interesting. I've been collecting it for three summers now and haven't had an issue yet. Something I'll keep in the back of my mind though if it happens. I wonder if the bacteria was coming from another source. Mind you I live in an area where the roofs are exposed. No trees or other obstacles so it stays dry until it rains.Careful if you collect from your gutters. I used to do that and it gave me root rot from the bacteria that lives on the roof. I used the 30% h202 from previous hydroponic grows to sanitize the water for a while, and eventually I just set up a different method of collection.