Where does drinking water come from?

By Carrie Chandler

Posted May 17, 2007

When you wake up in the morning and take a shower, brush your teeth, and have your morning glass of water, you rarely, if ever, wonder where that water comes from. For two-thirds of the residents in Vermont and New Hampshire, the water coming out of the faucet is from underground.

Less then one percent of the world’s unfrozen water is fresh, and nearly two-thirds of that amount is located underground. In the United States, 37 percent of the population relies on groundwater for its water supply. In New Hampshire and Vermont’s rural areas, nearly the entire population relies on groundwater.

But what exactly is groundwater? Quite simply, it’s surface water that has found its way underground and is located in the spaces between gravel, sand, sandstone, or fractured rock much the way water fills in the pores and spaces in a kitchen sponge.

In both states, most groundwater is found in fractured bedrock, made up primarily of gneiss and schist in Vermont and granite and schist in New Hampshire. In Vermont, 80 percent of private drilled wells draw from bedrock aquifers (as opposed to gravel aquifers), while in New Hampshire, the percentage is 85. Because bedrock aquifers are highly impermeable and the water they contain is stored only in fractures in the solid rock, they do not store large amounts of water per unit of area.

Sand and gravel aquifers supply water to the balance of private wells in the two states. These aquifers, made up of layered gravel that was sorted by size during the melting of the last glaciers, are usually found above bedrock aquifers. Because these aquifers are relatively porous, they store far more water per unit of area than bedrock aquifers, but because they are close to the surface, they are also more likely to become contaminated by runoff and pollution.

Depending on how deep the water table lies, the wells drilled into bedrock aquifers may require drilling to a depth of 500 feet or more. The water is either pumped out of the well, or, in the case of an artesian well, the pressure in the aquifer is enough to force the water up and out on its own. Even urban residents who don’t have their own private wells may rely on groundwater indirectly because many municipalities obtain their water from drilled wells.

Pumping groundwater out will deplete an underlying aquifer unless the aquifer is being replenished. Rain and melting snow are the primary sources of replenishment, sinking unseen into the ground either through bedrock fractures or seams of sand and gravel.

Although aquifers are underground, they are not necessarily protected from contamination. In New England, the biggest contributors to groundwater pollution are leaking underground storage tanks, leaks at hazardous waste sites, and phosphorus and nitrogen runoff, which comes from human waste and the misuse of fertilizer.

These human-induced threats have contaminated five percent of New Hampshire’s groundwater wells; however, the primary contaminants to the state’s groundwater are from natural sources. According to the Groundwater Protection Council, an association of groundwater protection agencies, 15 percent of the wells in the state contain iron and manganese, which present no threat to human health but do give off an odor and can cause an unpleasant taste. Radon poses a greater threat: between 75 and 90 percent of the state’s wells containing more than the proposed EPA standard.

Over-withdrawal is another threat. According to Jon Groveman, water program director of Vermont Natural Resources Council, “Williston, Vermont, is a community that has seen tremendous growth by Vermont standards over the last two decades. As housing subdivisions were built in one area of Williston, they were all tapping into the same aquifer for water supply. Eventually, the aquifer reached its limit and homes began seeing their wells run dry.”

Subdivisions aren’t the only developments that compromise aquifers. Industrial-scale bottled water operations also affect aquifers in New England, and the water they withdraw is effectively removed from the community. Bottled water is taken from the watershed and shipped throughout the United States; once it’s gone, it’s gone. Water used in households, on the other hand — for agricultural purposes, and even for some manufacturing processes — is typically returned to the same watershed by way of a septic system or sewage treatment plant.

Although we don’t live in the West, where the preciousness of groundwater is everyday news, New England faces the same basic problems as the western states: overuse and contamination.

“Water is not a commodity like other earth resources such as metals, minerals, oil, and gas,” says Groveman. “There are substitutes for these resources. However, if our fresh water supply is compromised, there is nothing that can substitute for water.”

Carrie Chandler is a freelance writer living in Barre. Illustration by Adelaide Tyrol.

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