Most residents use private wells, and both towns are reliant on natural groundwater.

The Charles River flows between Dover and Sherborn and affects the groundwater. A study released this summer by the Sherborn Groundwater Committee says that Sherborn has "a strong vested interest in the 'health and well being' of the Charles River."

Leaders in both towns understand the need to protect this resource.

As James Fleming of the Dover Open Space Committee told the Dover-Sherborn Press in October, "The bottom line is the core issue of water." Approximately one-third of Dover consists of protected land; it's just one of many measures taken to ensure good quality groundwater.

So far, protection efforts seem to be doing a good job.

Kathy Baskin, an engineer and project manager at the Charles River Watershed Association, feels that Dover and Sherborn are in pretty good shape.

Regarding the health of the Charles River, the "Dover-Sherborn area is a pretty good area," she said.

Robert Homer, Dover town engineer, agrees. One of his main responsibilities is keeping an eye on the town's water supply.

"We're an oasis," he said.

Oasis is an apt description since both towns rely on private wells and septic systems, creating a degree of self-sufficiency. What people take from the groundwater supply, they put back in. "In our minds, that's the best scenario," said Baskin.

But Dover and Sherborn may be two good apples among a slew of bad ones.

There are 35 municipalities on the Charles River Watershed, including highly urban areas at the end of the river such as Boston and Cambridge.

"Some towns nearby are sort of in a bad situation," said Baskin, citing towns such as Wellesley, Natick and Westwood.

According to her, over the past eight years, 1 million gallons of raw sewage has been removed from the Charles River every day.

The problem is sewer systems. Some mistakenly leak into the river, and many more take valuable water out of the Charles River Watershed.

Some towns withdraw heavily from local aquifers, but have sewers that flow into other towns or watershed systems. They don't replenish what they take.

Baskin also described the process of "ìnfiltration," in which groundwater seeps into underground sewer pipes that aren't totally tight.

At the Deer Island water treatment plant in Boston Harbor, said Baskin, only one half of incoming water is actual wastewater; the other half is infiltration water.

Such towns are literally flushing water away; in this context, Dover and Sherborn are examples of responsibility, since they replenish what they take.

Furthermore, because water flows beneath towns with total disregard to political boundaries, neighboring towns withdraw from shared aquifers.

Any single entity that withdraws at least 100,000 gallons of water per day needs a permit from the Massachusetts Department of Environmental Protection. (Neither Dover nor Sherborn is subject to these permitting regulations since they don't withdraw such amounts.)

The situation has created what Baskin calls a "gold rush" to the aquifers. "Whoever can get there first and get their permits authorized by the state gets the water," she said.

In Milford, for instance, the Milford Water Company has rights over the headlands of the Charles River, said Baskin. The company's water withdrawal can affect the entire river.

Baskin predicts contention between towns in the future over issues of water rights. Small towns such as Dover and Sherborn, which don't compete for DEP permits with larger towns, could nonetheless find their water supplies influenced by such competition.

With such neighbors, is the groundwater safe? According to Homer, "There's no immediate threat to groundwater."

The most catastrophic thing that could happen would be a major accident at a gas station. Gas and fuel are "the most visible source of contamination for groundwater," he said. A major fuel spill could get into the storm drain system, causing problems.

Even so, such an event wouldn't be devastating to the towns.

According to Homer, most area homes have deep wells which are drilled deep into the bedrock. In contrast, shallow wells are dug down only about 20 to 30 feet, but these wells are less common. Because groundwater is filtered clean as it seeps through the ground, the shallower the well, the more subject it is to contamination and pollutants. "Deep wells are not subject to that sort of thing," Homer said.

Baskin said deep wells may be subject to contamination, but feels "it's hard to determine the impact" of such things. She agrees that deeper groundwater doesn't get as exposed to pollutants as shallow groundwater.

"Both towns are managing very well," said Homer. They're doing well because people in both towns make it that way. Town groundwater committees, open space committees, conservation commissions, snow removal committees and an array of other groups remain diligent about providing an environment in which groundwater is safe and forthcoming. As long as town residents and leaders continue to work towards this goal, groundwater should remain safe and readily available."