NEWPORT, R.I. — The ponds that supply the Newport Water System and its nearly 15,000 service connections with drinking water are impaired and don’t meet the federal requirements of the Clean Water Act.

The water coming out of customers’ taps is safe to drink, but the raw, untreated water coming from the system’s nine reservoirs — North and South Easton ponds, Gardiner Pond, Paradise Pond, St. Mary’s Pond, Sisson Pond, the Lawton Valley Reservoir, Nonquit Pond and the Watson Reservoir — is polluted largely by elevated levels of phosphorus, which can unleash a flood of problems. All of these ponds are on Rhode Island’s list of impaired waters.

“We’re not here because the public water suppliers are doing a bad job,” June Swallow, chief of the Rhode Island Department of Health’s Office of Drinking Water Quality, said at a March 31 meeting at the Newport Public Library. “The water is safe to drink, but there is a problem with the water before it’s treated.”

Newport Water’s reservoirs — seven on Aquidneck Island and one each in Tiverton and Little Compton — experience frequent algae and cyanobacteria (blue-green algae) blooms. State officials said the water is safe to drink because new and upgraded water-treatment facilities opened last year, but the quality of the water from the reservoirs in Portsmouth, Middletown, Newport, Little Compton and Tiverton remains a concern.

“Excessive phosphorus loading starts to change the ecosystem and public health and habitat concerns are created,” said Brian Zalewsky, of the state Department of Environmental Management’s Office of Water Resources.

Efforts to prevent excess phosphorus and other pollutants, such as nitrogen, from entering these drinking-water sources is being complemented by the recent completion of improvements at Newport Water’s two treatment facilities — upgrades at the Station 1 Water Treatment Plant on Bliss Mine Road and the construction of the new Lawton Valley Water Treatment Plant in Portsmouth. The work included the addition of advanced water-treatment processes at both sites. These treatment facilities became operational last year, and together some 40,000 pounds of carbon is being used to filter water from the district’s nine contaminated sources, according to Julia Forgue, the director of utilities for Newport Water.

Sources of phosphorus and nitrogen are varied, but are typically linked to stormwater runoff, pet waste left on the ground, geese waste, and agricultural and golf course fertilizers.

The multiagency effort is being conducted to ensure that the water quality in each of the nine reservoirs continues to be suitable for drinking.

“Our goal is to restore the water quality of these reservoirs and their watersheds,” said Elizabeth Scott, deputy chief of DEM’s Office of Water Resources. “There is an incredible amount of federal and state investment being made to evaluate these reservoirs and to determine how we can best protect and restore them.”

Though the quality of district’s “finished” water has improved, according to state officials, the quality of the raw water that necessitated these improvements remains a problem. The nine reservoirs are still nutrient-enriched and experience frequent algal blooms that impact aquatic life and the reservoirs’ use for drinking water. Protection of these source waters is considered by the Department of Health as the front line in protecting public health, and is essential to the long-term viability of Aquidneck Island’s water supply.

“Treatment plants are just one part of providing safe drinking water,” Swallow said. “It begins with source-water protection, and it includes community involvement and monitoring.”

DEM will be conducting bi-weekly monitoring of the nine reservoirs from May through October to gain a better understanding of the ponds’ water-quality issues. These waterbodies are connected by a complex network of pump stations and 170 miles of pipe.

Excessive algae abundance can cause a variety of problems to water supplies, including taste and odor, cyanotoxins and the formation of disinfection byproducts (DBP), according to the proposed report designed to address these problems. Both phytoplankton and cyanobacteria are, in part, responsible for the production of total organic carbon (TOC) that contains the precursors for DBP formation.

The Environmental Protection Agency (EPA) sets standards for controlling the levels of disinfectants and DBPs in drinking water, including total trihalomethanes (TTHMs). Trihalomethanes are typically formed in drinking water as a result of the chlorination of organic matter present naturally in raw-water supplies.

TTHMs are a group of volatile organic compounds, such as chloroform, bromoform, bromodichloromethane and dibromochloromethane, that form with time when the natural organics in water react with chlorine as it breaks down.

Many districts treat drinking water with a chemical disinfectant, such as chlorine, to inactivate pathogens that cause disease. While disinfectants are effective in controlling harmful microorganisms, they can react with organic and inorganic matter in the water to form DBPs, some of which can pose health risks at certain levels.

Some people who drink water containing TTHMS in excess over many years may experience problems with their liver, kidneys or central nervous system, and may have an increased cancer risk. The EPA standard for TTHMs is 80 parts per billion (ppb) and the Newport Water System is often above that threshold, according to both Swallow and Forgue.

The public health benefits of chlorine disinfection practices, however, are significant and well recognized, according to health officials. Consequently, one of the most complex questions facing water-supply districts is how to reduce risks from disinfectants and DBPs while providing increased protection against microbial contaminants.

The EPA standard for nitrogen is 480 ppb, and the district’s nine reservoirs have elevated levels as high as 1,306 ppb.

Reducing algae abundance in the reservoirs is expected to lessen Newport Water’s use of the advanced-treatment processes, and thus associated operational costs, according to state officials.