My main concern is avoiding mold, mildew and the red bacteria bloom you see in dirty waterers. After all, life depends on fresh, clean water and all manner of disease is borne through bacteria-laden water. Also, running water is quite different than stagnant water in a container.
AVOIDING EXPOSURE TO BLUE-GREEN ALGAE
Never drink untreated surface water, whether or not algae blooms are present. Untreated surface water may contain other bacteria, parasites or viruses, as well as algal toxins, that all could cause illness if consumed.
People not on public water supplies should not drink surface water, even if it is treated, during an algal bloom because in-home treatments such as boiling and disinfecting water with chlorine or UV and water filtration units do not protect people from blue-green algal toxins.
If washing dishes in untreated surface water is unavoidable, rinsing with bottled water may reduce possible residues. While we don't know if water containing low levels of blue-green algal toxins could leave residues on dishes, taking this precaution may help reduce possible exposures.
People, pets and livestock should avoid contact with water that is discolored or has scums on the surface. Colors can include shades of green, blue-green, yellow, brown or red. If contact does occur, wash with soap and water or rinse thoroughly with clean water to remove algae.
Stop using the water and seek medical attention if needed if symptoms such as skin, eye or throat irritation, allergic reactions or breathing difficulties occur while in contact with untreated surface waters. However, swimming, bathing or showering with water not visibly affected by a blue-green algae bloom is not expected to cause health effects.
Where to get more information
NYS Department of Health
Bureau of Toxic Substance Assessment
ph: 800-458-1158 ext. 2-7820
From this page:
http://www.health.state.ny.us/environmental/water/drinking/bluegreenalgae.htm
and another article:
http://www.ene.gov.on.ca/cons/5089.pdf