Good management of horses includes supplying drinking water that is clean. There are many reliable methods to ensure this is accomplished, depending on what method you choose to provide drinking water.
If you have buckets, troughs, or any type of automatic waterer that has standing water inside of it constantly, it is appropriate to keep an eye on it. In warmer months and climates, you may need to scrub algae from the water source on a regular basis. This is very important, as water that becomes infested with algae can develop an unpleasant taste for horses and they may reduce their water consumption.
With stagnant water, the potential for rodent infestation is also possible. Rodents, whether mice, rats, or even at times birds can find their way into and drown in drinking water thereby poisoning the water of horses needing to drink. The bacterium that come along with this situation, can cause salmonella poisoning and other potentially fatal diseases. A logical way to prevent this is to avoid standing water when possible.
Temperature also has a large factor in whether or not a horse will drink enough water. In hot climates or summer months, a horse is more prone to lose body weight because they do not drink enough water. This can cause problems with their digestion, temperament, and overall health. Warmer weather means that there are more chances of stagnant, high temperature water that is apt to produce algae and bacteria.
In the winter months, horses will refuse to drink water if it is too cold or frozen over. This can cause severe health related problems such as digestive problems and colic for the animals. Colic can make horses agitated and at times shorten their temperament towards people.
If a horse refuses to drink water, it will become malnourished. It will eat less because it cannot digest the food easily. Malnourishment cannot only be expensive to counter, it is can have deadly consequences.