Horses are generally good at detecting when water sources are not safe, but not always, so it is important to know some basics about water quality. Water quality can be affected by the amount of compounds in the water (including minerals, such as sulfur or iron), any noxious agents such as pesticides, or pathogenic bacteria. Water can be tested easily for total dissolved solids, pH, individual minerals and other compounds.
Ponds can be at risk of accumulating any runoff from neighboring farms, and if they are the horse’s sole source of water, they should be tested regularly. Ponds can also be at risk for developing blue-green algae. This is a noticeable blue-green sheen or scum that tends to bloom in hot months. Fresh blooms often smell like newly mown grass, while older blooms may smell like rotting garbage. The algae is really a type of cyanobacteria that can contain toxins that are dangerous to the horse (and other pets or livestock), potentially causing sudden death. Ponds can also be at risk of accumulating nitrates, which is of greater concern for ruminants such as cattle, but also, to some degree, for horses. If high amounts of nitrates are ingested, it can be converted to nitrates in the body, which competes with oxygen on hemoglobin.
Streams are a little better than ponds because, typically, compounds are less likely to sit and accumulate. That said, there is no knowing where the water is coming from and what it could contain.
It should be noted that if the stream or pond is on your property, you can have an impact on the runoff and risk for your water sources. Manure management plays an important role in keeping your nearby pond or stream clean. Runoff from the manure pile can reach the stream or pond either over the ground or through the soil. Depending on the horse’s diet, excess nitrogen or phosphorus can make its way into the manure and wet bedding, and can cause negative environmental consequences to water systems. Manure stockpiles should be kept at least 70 metres from water sources. Building a manure collection area with concrete floor, walls and drainage at a high point on the farm can help direct any runoff away from water sources. It is wise to have your farm’s water tested at least annually to be sure it is safe to drink.
If you are out on a trail, it is probably wise to avoid unknown ponds, particularly if they are stagnant or show any sign of blue-green algae. Streams are probably a little safer. If you know you are going to be out on the trail for a while, it is good idea to scope out some water sources before you head out.