Ah, Taz, where do you think these things come from? I've gotten everything from Daphnia to hydra to Copepods of various sorts, usually not within any reasonable time of adding plants or anything to the tank.
Anyways, I don't think most tap water places go through very thorough treatment. From what we learnt at school, it's mostly removal of metals, organics being consumed by bacteria and removal of nitrates which are considered the most vital. Things like RO, UV, distillation, all remove things like bacteria and viruses, but most cities don't do this for tap water.
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