Charles Stringer stands at the steep lip of the muddy grave, holding his breath as the crane lowers the giant concrete pipe into the earth. Two miles west of Lake Tawakoni, hardhats glint in the morning sun, as gloved hands and taut, dusty bodies maneuver the 18,000-pound water main into place.

For Mr. Stringer, Dallas' assistant director of water utilities, the graceful execution is almost enough to overshadow the frustrating reality: This pipeline is far too young to have failed. And in a city where workers buried the oldest waterlines well before World War I, officials dread pouring time and money into unexpected projects like this one.

The city's water and sewer pipes are designed to last 50 years. Already, more than half of the existing lines have exceeded this age limit, said Robert Johnson, director of water utilities. While some pipelines are 60 years old and working well, others have passed 90 years and are on a long waiting list for replacement.

"What we're dealing with here is an aging system," Mr. Johnson said. "We do have a backlog [of repairs]."

The 50-year design life is a ballpark figure, and most pipes are expected to reach their 70th or 80th birthday. But on average, Mr. Stringer said, Dallas' water pipeline network is older than it should be, and being replaced slower than it should be. Water and sewer lines are currently replaced at a rate of once every 150 years. That number should be closer to 75, he said. "It's too long, and the longest it's ever been," Mr. Stringer said.

This logjam has led to frequent main breaks, particularly in the summer. And in coming years, as the city attempts a major infrastructure overhaul, residents can expect to see even more. "It's true, we have a large number of main breaks per mile in this city," Mr. Johnson said. "And it may get worse before it gets better."

Dallas transports water from five reservoirs to customers across 700 square miles, pumping an average of 440 million gallons of water a day. In the summer months, water use peaks as high as 800 million gallons per day, putting a strain on the aging system.

The city's per-capita water consumption remains among the highest in the state and tops all U.S. cities of comparable size, a fact city officials attribute to commercial water use. With about 9,000 miles of mains, Dallas' water infrastructure is the fifth-largest in the country and will boast more than a billion gallons of water a day by 2010. "I think sometimes the magnitude of what we do gets lost," Mr. Johnson said. "The scale is hard to grasp."

Despite the city's size, Dallas' water infrastructure needs pale in comparison to some of the nation's oldest cities. Across the country, environmentalists and water experts fear that aging utilities could heighten contamination and health risks. In February, corroding service lines caused unhealthy levels of lead in drinking water in Washington, D.C.

This spring, lobbyists urged Congress to allocate $5 billion in the 2004-2005 budget for water and sewer improvements. Since the Clean Water Act was passed 30 years ago, federal funding for repairing water infrastructure has decreased by 70 percent. The Environmental Protection Agency warns there will be a $500 billion funding gap in the next 20 years if federal investment isn't increased.

"Dallas is younger than some cities, and it has been more diligent," Mr. Stringer said. "For a lot of cities, it's been 'Out of sight, out of mind'."

In Dallas, officials say, an emphasis on growth has put infrastructure repairs on the back burner. The city's history as a regional provider dates back to 1878, when Dallas first pumped water from the Trinity River. After battling serious droughts in the first half of the 20th century, city officials made a promise: Dallas would never run dry again. In the 1950s, they made a commitment to supply water not just to the city, but to its neighbors as well. As the region has grown, so too has this responsibility. The Dallas Water Utilities Department serves 2.3 million people across 19 cities. It will have an estimated 5.3 million customers by 2060.

Faced with a surging population and a tight budget, the department has chosen to spend its limited dollars nailing down future reservoirs instead of replacing older pipeline. "We have to be ahead of the curve and anticipate need," Mr. Johnson said. "Dallas may be good through the year 2025. Unfortunately, the next water resource may take 25 years to develop."

During the 1980s and '90s, the city's water infrastructure was quietly aging, Mr. Johnson said. But there had been no major consequences. "As old as the system is, it functions very well," Mr. Johnson said. "I don't think anyone ignored it, but it was not brought to the forefront."

Frequent main breaks in the late 1990s and early 2000s have forced city officials to reshuffle their priorities. In September, the department earmarked $700 million for infrastructure replacement over the next several years. And in April, City Manager Ted Benavides charged the city with replacing 50 percent of its water and sewer lines -- nearly 4,000 miles -- within the next 30 years.

"Before, we were in growth mode, and focusing our energies on that," Mr. Stringer said. "Now, we're starting to focus on the other parts, namely maintenance."

This year, water rates jumped 11.3 percent, bringing the average customer's bill to $39.05 per month. Next year, they'll rise 7 percent to 8 percent. And residents can expect to see a third jump the following year, to help fund a laundry list of improvements to the city's most decrepit lines. "We'll target the worst areas first, based on how much maintenance they've had," Mr. Johnson said. "We're aiming to replace 60 miles this year, then double that in following years."

Advanced technology is helping the department meet these goals by reducing the risk of major main ruptures. New sonic testing systems act an angiograms for the water arteries, emitting radio signals to get accurate readings on the smallest of leaks. Now, the department can "test and re-test" the city's biggest mains, Mr. Stringer said, catching and repairing pipe distress before it gets serious. City data suggest pipe leaks account for approximately 7 billion gallons of water per year.

And, Mr. Johnson said, his staff is developing plans for water conservation and re-use public service campaigns, strategies that could free up dollars for other projects. A conservation program with a 15 percent reduction in demand could extend available water supplies by three years, he said. "We are taking an aggressive stance toward conservation because it makes economic and environmental sense," Mr. Johnson said. "If we could get conservation at around 15 percent, financially, it would be the equivalent of having Lake Ray Hubbard paid for."

[COMMENT: This is a curious statement. Lake Ray Hubbard is about 30 years old. Hasn't it been paid for by now? R.]

Despite the age of much of the city's infrastructure, some newer pipelines have been more problematic. The raw water transmission line between Lake Tawakoni and its balancing reservoir failed on Dec. 31, at the tender age of 25. When the inspectors came out to check the break, they got more than they bargained for. Of the 16.2 miles of pipeline, 293 joints needed replacing -- nearly a tenth of the main.

On a recent weekday morning, 50 miles east of Dallas, contractors in Kaufman County admired their repairs on the 7-foot-wide Tawakoni pipeline, using a foreign sign language to talk over the panting machinery. The excavated pipes, large enough for a grown man to stand in, are left to crumble in patchy grass, the gaping Os of their mouths trimmed with rusty metal shards and thick, gnarled wires.

As Dallas' only water source outside the Trinity River Basin, Lake Tawakoni supplies a third of the city's water during the summer months and can provide up to 250 million gallons per day. In order to meet peak summer demands, the department sent out work crews to make immediate repairs -- to the tune of $18.2 million. The repairs, done at 80 sites along the line, are expected to be complete this month. For now, the city is taking no water from the lake and is securing an emergency permit to take extra water from Lake Ray Hubbard.

But the money is not as easy to replace. Mr. Johnson said the department will fund the project by pushing some others back a year -- he's just not sure which ones. "This isn't the kind of project you want," he said. "But it's critical to the city's water supply."

So far, the cause of the Tawakoni failure has not been determined. But it shows similarities to another premature main break in recent history. In February 2001, a 20-year-old water line from White Rock Lake ruptured, blasting nearby townhouses with millions of gallons of water. Tom Drake remembers it like it was yesterday -- the wall of water that broke through his patio doors and hardly gave him time to save himself, let alone his belongings. Mr. Drake had homeowners insurance but still paid more than $12,000 out of pocket. And everything he owned under 3 feet tall -- from furniture to family photographs -- was ruined.

"The city never paid a cent," he said. "It was a bad experience, and the way they handled it was unbelievable." But the worst part, Mr. Drake said, is that homeowners never got a report from the city on what caused the mess. "They promised they would announce it, and they haven't," he said. "They need to be very sure this kind of thing never happens again."

City officials say they have completed the White Rock investigation. The city attorney's office has not decided whether the report should be made public, citing legal implications. But Mr. Stringer said the report "didn't come to any firm conclusions". There are many factors that can lead to a main failure, he said, from improper installation to pipe corrosion.

Mr. Stringer said a structural analysis will be performed on the Lake Tawakoni line as soon as the repairs are complete. But there's no promise it will produce answers. "It doesn't necessarily mean [the pipes] have defects," he said. "Sometimes they fail prematurely and we just can't tell why."

[COMMENT: This article is accompanied by a drawing that shows the five reservoirs from which Dallas gets its water: Lake Tawakoni, Lake Ray Hubbard, Lake Ray Roberts, Lewisville Lake and Grapevine Lake. A future pipeline to Lake Palestine is shown, as is Lake Fork Reservoir, which is close enough to Lake Tawakoni to possibly supplement that water. No future pipeline to Lake Fork is indicated. R.]