A MAJOR reason why our fresh water is contaminated is humans. First of all we pollute the body of water, with garbage. Sometimes this happens on purpose, but most of the time it is by accident. For example, when your house gets flooded debris can come through and eventually end up in fresh water systems. Sometimes, it is the lack of good building structures. For example, the piping might not have been placed correctly, so all that dirty water contaminates the fresh water near you. Sometimes it is out of our control, such as silt run off, which happens because of the rain.  However,  we CAN make sure there are no leaks in our toilets or sinks and be sure NOT to throw away any harmful liquids. This would be pollution.