One-third of the water treated at D.C.'s Blue Plains Wastewater Treatment Plant is actually sanitary water coming from such sources as deteriorated water pipes and leaky household faucets and toilets, according to a new report by a team of George Washington University urban planners.

The disrepair of water lines, coupled with a per capita water consumption rate that the report said is triple that of most other cities, is placing an unnecessary burden on Washington's already strained wastewater system and is increasing wastewater treatment costs by thousands of dollars a year, according to the study.

Dorn C. McGrath, the GW professor who supervised the research, said yesterday that low water and sewer rates, plus a history of erratic billing for water use, have encouraged an unusually high rate of water consumption in the District.

The report said city officials should consider increasing water and sewer rates to cut down on consumption and to finance the improvement of the existing systems.

McGrath said D.C. residents consume 200 to 250 gallons of water per person per day, compared to a per capita rate of 100 gallons or less in other cities of similar size.

The study, which examines the city's "infrastructure" -- areas such as water, sewer and transportation which are considered essential to daily functions -- concludes that Washington, like many other major cities, continually approves new construction while neglecting the repair and maintenance of its existing buildings and roads.

It found longstanding disrepair at many of the city's libraries, recreation centers and firehouses. The problem is especially critical at the city's fire stations, the report says, because one-third of the stations are more than 70 years old and many are so small that some of the newer, more sophisticated firefighting equipment cannot fit in them.

Acting Assistant Fire Chief Harry Shaffer said yesterday there are certain types of firefighting equipment that "would have difficulty getting in and out of the older fire houses," but that he did not believe the situation created a safety problem.

The George Washington report says that the city's Department of Environmental Services makes no periodic tests of water valves and fire hydrants to insure that they are in working order.

McGrath said that when a water main burst at 12th and K streets SE, DES officials had difficulty finding working valves which they could shut off to isolate the break. Consequently, thousands of gallons of water flooded into neighborhood streets and house basements before the water was cut off.

The chief of the DES water and sewer management division could not be reached for comment yesterday. A 1980 report by the privately-run Federal City Council was also highly critical of the state of the city's water system.

The report says the city needs to develop "an effective comprehensive plan" so that the existing water and sewer systems can keep pace with the amount of development and new construction approved.

It also recommends that the District place a higher priority on maintenance and repair in its capital improvements program.

"It's penny-wise and pound-foolish to defer maintenance," McGrath said yesterday.