The way their water bills look, you'd think residents of Prince George's and Montgomery counties had Perrier flowing from their faucets.

The 1.6 million customers of the Washington Suburban Sanitary Commission pay some of the country's steepest prices for water -- about $21.24 a month for a family of three, and that's not including the cost of sewer service. The same family would pay $16.50 for the same amount of water from the District.

And WSSC's rates are going up 3 percent July 1, when a family's average quarterly bill, according to WSSC's estimates, will be $136.13, more than it would pay for the same amount of water in Fairfax County ($88.40), Arlington County ($101.56), the District ($115.42) or Howard County ($124.08). The increase will come on top of a $30-a-year surcharge that the state added to water bills to help pay for modernization of wastewater treatment plants.

The disparity is even more striking when one looks at the drier parts of the West. A family of three using the same amount of water in Yuma, Ariz., where the average annual rainfall is three inches, can expect to pay $13.35 per month for water. Los Angeles, where political machinations surrounding the water supply inspired the 1970s film classic "Chinatown," currently charges $16.93. In Las Vegas, it is $14.60.

There are prominent exceptions. Seattle, with a legendary wet season that brings an average 38 inches of rainfall per year, has among the nation's highest water rates -- $34.80 a month. Boston, at $25.80, is costlier than WSSC.

Therein lies one of the little-known facts about water: Its price often has nothing to do with the available supply. Instead, say utility experts, costs are driven by myriad factors: maintenance, personnel, security, debt, federal regulation and subsidies and mismanagement.

Western states have formed "water banks" to ensure that no area is critically short of water. They also promote water conservation more aggressively than other regions, easing pressure on the supply. Drought still affects the West, but so far it has not driven up the cost of water, which is often well below prices on the East Coast.

The main budget item that pushes up costs is maintenance. Water systems with thousands of miles of pipes require constant attention, particularly in the East, where infrastructure is often old and buried under heavily developed areas, making excavation and repair expensive.

"The pipes that are in the ground, many of them have been there for at least 100 years, and they are nearing the end of their useful life," said Melissa Stanford, a researcher at the National Regulatory Research Institute at Ohio State University. "As those pipes begin to be relined and replaced, that is definitely driving costs upwards."

In theory, costs would increase gradually to accommodate maintenance and replacement of pipes. But in practice, many utilities have put off the day of reckoning as long as possible. A 2002 study by the Environmental Protection Agency showed that deferred maintenance has allowed water suppliers to keep their prices low and that a sudden surge in rates may take consumers by surprise. The EPA estimated that utilities across the country would need $300 billion to $1 trillion to upgrade treatment facilities, meet water quality standards and accommodate population growth.

WSSC officials say they've maintained their 10,000 miles of pipes over the years, allowing them to hold rates fairly steady. This year's 3 percent rate increase is the first since 1997.

"Most people are going to catch up to us," predicted Thomas C. Traber, WSSC's chief financial officer. "We made it a point to maintain our system."

Atlanta did not. In 2003, a federal court ordered the city to repair its dilapidated water system at a cost of $3 billion. The mayor wrote a letter warning Georgia's governor that residents could expect a 45 percent increase in 2004, another 45 percent increase in 2005 and 11 percent increases in 2006, 2007 and 2008 unless the city received aid from the state and federal governments. The city is debating adding 1 percent to the sales tax to roll back the rate increases.

While WSSC does not expect such drastic measures, it is contending with debts incurred two decades ago. The agency plans to spend 46.9 percent of its $465 million operating budget for 2005 on debt service. Much of it, Traber said, was taken on during the 1980s and early 1990s, when the population of the Washington suburbs rapidly expanded.

The growth was good for the economic health of the region, but not for WSSC's bottom line. It borrowed heavily to finance infrastructure for development. Since 1994, Maryland law has required developers to pay for water lines and other services.

The agency is $1.6 billion in the red, but Traber said that there was no cause for worry and that the agency was well below the $4.8 billion debt ceiling imposed by law.

The debt is "not bad," Traber said. "We'd love to have it lower, but we don't see it dropping appreciably."

WSSC is also paying, in time and treasure, to cast off a reputation for misspending and corruption that goes back more than a generation. As an agency jointly governed by Montgomery and Prince George's counties, it has contended with surpluses of patronage and deficits of accountability.

In 1976, five WSSC inspectors were indicted by a Montgomery grand jury on 123 counts of bribery. The indictments were dropped because state law then specifically barred bribery of state, county and city officials but not of employees of a bi-county agency such as WSSC.

In 1984, the agency spent $54 million on a major water tunnel to serve Prince George's County. It leaked on its first test, and engineers later found more than 6,000 cracks, a debacle that eventually cost WSSC more than $100 million.

In 1991, the agency's new Laurel headquarters, an opulent glass office building colored deep blue, opened $4 million over budget.

In 2002, a former WSSC manager was charged with paying a consultant more than $200,000 in bogus fees; both men recently pleaded guilty in federal court.

Even now, the agency grapples with financial irregularities. It was recently revealed that Prem Agarwal, a member of WSSC's governing commission appointed by Prince George's County Executive Jack B. Johnson (D), did nothing to stop his own company from receiving a $1.4 million contract on a utility project.

WSSC's general manager, John R. Griffin, said part of the reason the agency hasn't had a rate increase since 1997 was that he was trying to restore confidence in WSSC's management.

Even if he succeeds in that, he has to contend with a host of significant costs.

The agency pays its 1,500 employees $75.3 million a year in salaries and wages. Health care costs increased 15 percent in one year. WSSC also has earmarked $100 million to spend on security improvements around its water processing facilities.

There is also inflation.

"When you don't adjust rates for inflation, it's a rate decrease," said Griffin, who added that he planned to propose another 3 percent rate increase next year, then go two years without another increase.

"To me, it's necessary and probably will be periodically something we do," Griffin said.

The last source of financial angst comes from another utility. Pepco is seeking a rate increase for electricity that could cost a typical Maryland residential customer about $150 more in the coming year, as deregulation of the electrical industry goes into effect and price caps are abolished.

WSSC operates two power-guzzling water filtration plants, four reservoirs, six wastewater treatment plants and the Blue Plains Water Pollution Control Plant. Pepco's rate increase will cost it millions of dollars.

As it happens, even utilities have to pay the utility bill.

John R. Griffin, WSSC's general manager, said he plans to propose another 3 percent increase next year on top of the one this year. The last increase was in 1997. This water filtration plant on River Road near Potomac is one of two WSSC operates to feed its 10,000 miles of water pipes and 1.6 million customers.