What Are Acceptable Levels of Ammonia in Water?

Ammonia is a compound made up of nitrogen and hydrogen, with the molecular formula NH3. At room temperature it's a gas but because it can form hydrogen bonds, it dissolves extremely well in water. In nature, ammonia is produced by nitrogen-fixing bacteria that convert atmospheric nitrogen into a form that plants can use. It's also excreted by fish and certain other animals. Ammonia in water is toxic to fish even at low levels and at higher levels can be toxic to humans as well.

  1. Function

    • Proteins and nucleic acids like DNA are both important types of molecules in cells that contain nitrogen. When these molecules are broken down, ammonia is released as a toxic byproduct. In humans and other mammals, this ammonia is next converted to a safer waste product called urea, which is then excreted in the urine. Fish, however, excrete the ammonia without converting it first. Some bacteria also fix atmospheric nitrogen to produce ammonia; other microorganisms that consume dead or decaying organic matter release ammonia as part of the decomposition process. Various other bacteria turn ammonia in soil into nitrites and nitrates, thereby playing a key role in sustaining plant life--and hence all other life on land.

    Effects on Fish

    • Ammonia is highly toxic to fish even at very low concentrations; levels of 0.2 to 0.5 parts per million are enough to kill some aquarium species. The precise level of ammonia that will suffice to kill a fish depends on the temperature and pH of the water. Given the serious threat posed by ammonia to your fish, however, the best general rule is that it shouldn't be present at levels you can detect. If you can detect ammonia in the aquarium with a test kit, the level is probably too high.

    Effects on Humans

    • Humans are not quite so sensitive as fish to ammonia in their water supply; moreover, ammonia levels in most natural water sources are very low. According to the World Health Organization (WHO), the level found in groundwater is typically below 0.2 mg per liter. The Oregon Department of Human Services warns that long-term consumption of water with levels over 1 mg per liter may cause damage to internal organs over time. The National Academy of Sciences recommends a standard of 0.5 mg per liter or below for drinking water as a general rule.

    Prevention/Solution for Humans

    • Unfortunately, ammonia is difficult to filter from drinking water; reverse osmosis, distillation or ion exchange systems can remove it but are often expensive. Disinfecting water with chloramines can increase ammonia levels. The presence of substantial ammonia in drinking water may point to contamination with sewage, animal wastes or fertilizer runoff, since high levels are otherwise rare in unpolluted water. If your water source is contaminated, the best and simplest solution may be to find another appropriate source or supply.

    Prevention/Solution for Fish

    • Adding too many fish medications, using a filter that's too small or improperly cleaning the filter are common causes of ammonia accumulation in fish tanks. Chloramine-treated tapwater is also another possible source of ammonia in your fish water. It's important to remove dead or decaying matter from the tank, clean the filter regularly and monitor for ammonia using a test kit--kits like these are available in most pet stores.