The maximum level of phosphorus in reservoirs used for drinking water is no higher than 0.025 milligrams per liter, per the United States Environmental Protection Agency's recommendation. While phosphorus is generally considered safe for human consumption, extremely high levels may cause digestive problems due to toxicity.
Phosphorus is a naturally occurring element necessary for the growth of plants. Most phosphorus in water is taken up by plant life, but it can cause an overgrowth of algae and other water plants in rivers and reservoirs. Increased bacterial growth and toxins in the algae may be harmful to humans who come in contact with the water, eat contaminated fish or drink polluted water.