Hundreds of miles of water mains, some as large as 8 feet, are buried under Montgomery County and the region’s water and sewer utility has reprised a warning that if a big one breaks in a densely populated area, nearby buildings and people could be endangered by the power of millions of gallons of water spewing forth.

The Washington Suburban Sanitary Commission, which provides service to 1.8 million people in Montgomery and Prince George’s counties, this month is considering new rules that would require developers to build at least 80 feet away from larger, high-pressure lines or undertake extra engineering steps to shore up and protect buildings. A rupture, some engineers calculate, could create a crater 50 feet in diameter, launch debris such as dirt and concrete as far as 210 feet and water could flow from the break at upwards of 90 mph.

Debate about the potential danger, reported in 2008 by The Gazette’s Margie Hyslop, has been largely dormant for four years. This year’s mild winter was relatively kind to buried pipes and breaks caused by freezing and thawing — a problem out of sight is often out of mind.

For most customers, reliable water service is an afterthought and engineering details are eye-glazing. Only when the toilet doesn’t flush or rates increase is there a consumer outcry (on July 1, rates will increase about $5 a month for a typical customer under a budget approved last month by county councils in Montgomery and Prince George’s). But these changes are critical as part of a long-term program to maintain life-sustaining infrastructure.

Engineers are prudent in flagging the potential hazards if there’s a break in the 145 miles of larger concrete water mains and in proposing changes to the so-called setback regulations. This isn’t a case of “Chicken Little.”

Since 1996, the WSSC notes there have been five major “failures” in its larger pipes, including a break in a 5-foot line under River Road in December, 2008. That episode, which made national news, required swift-water rescuers using a helicopter to pull people to safety from their partially submerged cars and refocused attention on the WSSC high-tech pipe monitoring program.

Developers don’t like the new rules, which could drive up costs and make some projects impractical without special engineering features to protect buildings.

One estimate puts the cost of replacing larger water mains, vulnerable to catastrophic rupture, at nearly $2 billion. For a utility that this year plans to replace or refurbish 46 miles of its 5,500 miles of water mains and 55 miles of sewer lines, a large-scale replacement program for the bigger mains is simply impossible.

One review, in 2008, found that there are almost 700 buildings in Montgomery and Prince George’s counties that are closer to buried pipes than the 80-foot setback requirement and 200 are at a “heightened risk” because of their proximity to the buried lines.

New buildings need a larger buffer zone, according to the WSSC. The revised regulations, scheduled for a vote by the commission next week, provide a safety break. And a compromise would allow buildings within the buffer if there are extra safety features incorporated in the design.

Approving the new regulations will be an important step in providing reliable water service for a fast-growing region for decades to come.