Bloomington Water Is Moderate — Here's What It Costs You Each Year

Why Is Bloomington Water So Moderate?

Bloomington sits on a pretty interesting piece of geology. The city pulls its water from groundwater, specifically tapping into the Jordan Sandstone, Prairie du Chien Group, and Tunnel City-Wonewoc Sandstone aquifers. These are deep, ancient formations that lie beneath the Twin Cities metro area, and they tell a story that’s different from what you’d find in, say, limestone-heavy parts of the country.

Here’s the plain-English version. The Jordan Sandstone is exactly what it sounds like: a massive layer of sandstone deposited hundreds of millions of years ago when this region was covered by shallow seas. Sandstone is mostly quartz grains, and quartz is chemically stubborn. It doesn’t dissolve easily in water, so it contributes very little calcium or magnesium. The Prairie du Chien Group is a mix of dolomite and sandstone. Dolomite does contain magnesium and calcium, so it adds some hardness, but the sandstone layers dilute that effect. The Tunnel City-Wonewoc formations follow a similar pattern, more sand than carbonate.

So what you end up with is water that picks up some mineral content as it moves through those dolomite layers, but not nearly as much as water that spends its whole journey in pure limestone. That’s why Bloomington lands at 5.2 GPG, or about 89 ppm. That’s classified as moderate, and it’s right in line with what you’d expect from these mixed sandstone-carbonate aquifers. The water isn’t soft by any stretch, but it’s nowhere near the “very hard” category above 10.5 GPG that plagues so many Midwest communities. You’re getting the middle ground, geologically speaking.

How Bloomington Compares to Nearby Cities

Bloomington’s 5.2 GPG puts it in a fairly comfortable spot relative to the broader metro area. The city’s Public Works department manages the supply, and because the source is these deep sandstone aquifers, the hardness stays relatively consistent year-round. Surface water supplies, by contrast, can swing with the seasons, especially during spring runoff or heavy rains.

The key thing to understand is that many surrounding communities in the southwest metro draw from similar aquifer systems. Some of those cities sit over portions of the same Jordan Sandstone and Prairie du Chien formations, so their water chemistry is broadly comparable. That said, the exact hardness can vary from one well field to another, even within a few miles. Aquifers aren’t uniform bathtubs of water; they’re layered, fractured, and the mineral content shifts as you move across the formation.

Compared to cities that rely on the Mississippi River or other surface sources, Bloomington’s groundwater tends to be more stable in its mineral content. Surface water picks up whatever it encounters along the way, and treatment plants often have to adjust their processes to account for changing conditions. Groundwater from these deep aquifers has already been filtered through hundreds of feet of rock, so what arrives at the tap is more predictable.

If you live in Bloomington and have visited a friend’s house across town, you might have noticed their water feels different. That’s not you imagining things. Well depth and which specific formation a particular well taps into can shift hardness by a couple of grains per gallon. But the big picture holds: Bloomington’s moderate hardness is a direct result of the sandstone-heavy geology beneath it, and that’s the whole story.

How does Bloomington stack up against the rest of Minnesota? It's moderate at 5.2 GPG — Rochester, Minneapolis, and St. Paul sit nearby with different numbers. See the full hardest-water ranking for context.

See where Bloomington sits on the Minnesota water hardness map →

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