Behlen Energy Free Stock Tank Waterer

How they work:

Heavy foam insulation keeps water at the perfect temperature, regardless of conditions.  Ground water enters the unit between 48ºF and 56ºF, where it remains until the waterer is opened by the animal.  As the animal drinks, new water enters through the automatic valve and mixes with the water already in the waterer, so it is constantly replenished and prevented from freezing.  The water in the waterer is kept in the dark, which prevents algae growth.