Somerville Water Is Soft

Why Is Somerville Water So Soft?

The short answer is that Somerville doesn’t pull its water from local ground. The city is part of the Massachusetts Water Resources Authority (MWRA) system, which supplies wholesale water to dozens of communities in the Greater Boston area. That water originates as surface water, not from wells or aquifers beneath Somerville itself. The MWRA’s primary supply comes from the Quabbin Reservoir in central Massachusetts, with the Wachusett Reservoir serving as a secondary, backup source. You’re not imagining it: at 0.64 GPG (11 ppm), Somerville’s water is classified as soft, and it’s soft because of where that rain and snowmelt lands and flows, not because of anything under the city streets.

Here’s the geology that matters. The Quabbin and Wachusett watersheds sit on the hard, crystalline bedrock of central Massachusetts. This is ancient igneous and metamorphic rock, think granite, gneiss, and quartzite, that formed deep in the earth’s crust hundreds of millions of years ago. Unlike the softer sedimentary limestone that dominates the Midwest and parts of the South, these rocks are chemically resistant to dissolution. Rainwater, which is naturally slightly acidic from dissolved carbon dioxide, picks up minerals as it seeps through soil and over rock. But when that water runs across granite and gneiss, there is very little calcium carbonate to dissolve. Limestone is essentially compressed calcium and magnesium; granite is mostly silica and feldspar. So the water that fills the Quabbin Reservoir carries a fraction of the hardness minerals that groundwater in limestone country would pick up. The result is water that starts soft at the source and stays soft through treatment and the long pipeline ride east to Somerville.

The reservoirs themselves also play a role. Surface water in a large, deep reservoir has a shorter contact time with mineral-bearing soil than groundwater that has spent years percolating through an aquifer. The water in the Quabbin is relatively young, it falls as precipitation, flows through forested streams, and sits in the basin before treatment. That short residence time over resistant bedrock means the dissolved calcium and magnesium load stays low. It’s a completely different story from, say, a deep well in Florida tapping into the Floridan Aquifer, where water has had centuries to dissolve limestone. Somerville’s water simply never gets the chance to become hard. That’s the whole story: soft bedrock, surface water, and a short journey.

How Somerville Compares to Nearby Cities

Because Somerville buys its water wholesale from the MWRA, its supply is essentially identical to that of neighboring communities that are also MWRA customers. If you live in Somerville and have a friend in Cambridge or Boston proper, you’re both drinking from the same regional tap. The water leaving the MWRA treatment plants is blended and consistent, so the hardness you measure in Somerville, 0.64 GPG, is going to be in the same ballpark as what comes out of the faucet in those adjacent cities. There’s no separate local well field or independent supply giving Somerville a different mineral profile from its neighbors. They share the same source, the same treatment, and the same soft character.

That said, there can be small differences at the tap, and they usually come from the pipes, not the source. Water sitting in older distribution mains or in a building’s internal plumbing can pick up trace amounts of metals, but that doesn’t change hardness in any meaningful way. The calcium and magnesium content is set at the reservoir and treatment plant level. So when you compare Somerville to nearby towns that draw from the MWRA system, you’re comparing the same water delivered through different pipes. The hardness is going to be soft across the board, typically well under 1.5 GPG for MWRA communities supplied by the Quabbin and Wachusett reservoirs.

The contrast becomes stark only when you look outside the MWRA service area. Towns to the south and west that rely on their own local wells, particularly those drilling into the sedimentary basins of eastern Massachusetts, can see noticeably harder water. But within Somerville’s immediate ring of neighbors, the story is uniform: soft surface water from central Massachusetts, delivered through a shared regional system. If your water seems to lather easily and leaves little scale on your kettle, that’s not a quirk of Somerville specifically. It’s the signature of the Quabbin, and it’s the same water your neighbors in Medford, Arlington, and Everett are getting too.

How does Somerville stack up against the rest of Massachusetts? It's soft at 0.64 GPG — Cambridge, Worcester, and New Bedford sit nearby with different numbers. See the full hardest-water ranking for context.

See where Somerville sits on the Massachusetts water hardness map →

Want the broader explainer on what hardness actually is and how it behaves? Read hard water vs. soft water, explained.