Why Your Office Water Tastes Different Every Season (in Madison, It's Not the Reason You Read About)

Updated September 2026. This post replaces three earlier ones (two on summer, one on winter) that told the generic story with no sources; they now redirect here. The spring version has its own post.

Every season somebody in a Madison breakroom tells me the water has changed. In July it is "more chlorine." In January it is "kind of metallic." They are usually right that something changed. They are usually wrong about why, because the explanation they have read was written for a city that drinks from a lake.

I sell water systems for a living, so weigh that. But I would rather explain what actually happens in Madison than repeat the version that sounds better.

The story you have read is about Lake Michigan

The seasonal-water article you find online goes like this: in summer, warm reservoirs grow algae, the algae produce compounds that taste musty, and the plant fights back with more chlorine and more carbon; in winter, cold water slows the treatment chemistry, so the plant doses differently. Your taste buds track the calendar.

That is a real story, and it is happening in Wisconsin right now, just on the other side of the state. Racine's water utility put out a seasonal taste and odor FAQ this summer explaining that the earthy taste in its tap water comes from geosmin and MIB, "produced by certain algae and other naturally occurring organisms in the lake," that "seasonal taste and odor events can affect water systems that draw from lakes and reservoirs, including Lake Michigan," and that people "can detect these compounds at extremely low concentrations, far below levels that pose any health concern." The utility's fix is activated carbon treatment, more hydrant flushing, and waiting for lake conditions to change. Same FAQ notes that neighboring cities on the same lake may not notice it at all, because intake location and treatment differ.

Lake-fed systems are a minority in Wisconsin but they serve a lot of people: the DNR's 2025 drinking water report counts 60 lake-supplied systems serving 32.2% of the state, mostly Milwaukee, Racine, Kenosha and Green Bay. If your office is in one of those, the algae story is your story.

Madison is not one of those.

Madison's water is 50 degrees in July and 50 degrees in January

Madison Water Utility pumps everything from a deep sandstone aquifer through wells 500 to 1,100 feet down. No lake intake, no reservoir open to the sun, no algae. The Wisconsin Geological and Natural History Survey's groundwater temperature map puts Dane County's average well water at 50.4°F, and the whole point of groundwater is that it does not know what month it is.

So the "warm water grows algae" mechanism does not exist here. What does change with the season in Madison is three other things, and the utility documents each of them.

Summer: you may be drinking from a different well

This is the one almost nobody knows. Madison's 2020 Water System Master Plan says demand "in the summer can be almost double the demands in the winter," and to meet it the utility runs wells it keeps off the rest of the year: "Unit Wells 8, 17, 23, 27 and 28 are seasonal wells, meaning they are generally off during the winter." The same document says outright that "based on water quality, some unit wells are operated throughout the year and others seasonally."

Each well draws from its own spot in the aquifer, and they are not identical. The utility publishes a separate water quality report for every well because iron, manganese, hardness and chloride differ from one to the next. The city-wide figure for hardness is 18 to 20 grains per gallon; Well 14 alone tests at 34. When a seasonal well comes online in June and starts feeding your part of the city, the water in your breakroom is, in a literal sense, different water than it was in March. That is the taste change people notice in summer. Not chlorine dosing. Blending.

You can look up which wells serve your address on the utility's site, and the report for each one. If your building sits in a zone where a seasonal well comes on, you now know why July tastes different.

Summer, part two: chlorine fades faster in warm pipes

Madison adds about 0.3 milligrams per liter of chlorine at each wellhead, a low dose that is there to keep the mains clean. What you taste is whatever is left when the water reaches you, and that depends on temperature. An EPA issue paper on distribution systems states that chlorine decay kinetics increase at higher temperature: residual disappears faster as water warms and as it travels further.

The well water starts at 50°F, but the mains under a sun-baked street, and especially the pipes inside a warm building, are not 50°F in August. So the summer effect in Madison runs the opposite direction from the lake-city story: the chlorine you taste tends to be lower in summer, not higher, because more of it has reacted away by the time it reaches your glass. The thing that goes up in summer is the mineral and iron character from whichever well just came online.

Winter: the salt

Winter is where Madison has a seasonal water story that is genuinely its own, and it has nothing to do with treatment chemistry.

Road salt does not stay on the road. The utility's own page on road salt and Madison's drinking water reports salt infiltration at five of the city's 22 drinking water wells. The worst is Well 14 on University Avenue, which runs year-round and serves Spring Harbor, Sunset Village, Regent, Shorewood Hills and part of the UW campus. Its 2025 report puts sodium at 66 mg/L against an EPA guideline of 20 mg/L for people on restricted-sodium diets, and the utility projects that chloride there will cross 250 mg/L, "the level at which water begins tasting salty to most people," within 17 years. Wells 6 and 16 are on the same path, about 40 years out. The city has spent $220,000 on a borehole study to find where the salt is getting in.

This is not a January-versus-July difference. The aquifer moves too slowly for that; the salt you taste at Well 14 fell on University Avenue years ago. It is a slow ratchet that has been running for decades, and it is why an office near Hilldale can have water that reads faintly "flat" or "mineral" year-round while an office on the east side does not. Every winter adds to it.

Winter, part two: less chlorine decay, more chlorine taste

The same EPA temperature relationship runs the other way in cold months. When mains and building pipes are cold, chlorine reacts more slowly, so more of the wellhead dose survives to your tap. If your building is close to its well, the chlorine note you notice in February is that. The utility's FAQ says a glass left standing loses the chlorine smell within about 12 hours, and the Racine tip list says the same thing for a different reason: refrigerate it, let it sit, drink it cold.

Spring and fall: flushing

The one thing that does hit on a schedule is hydrant flushing. The utility runs a unidirectional flushing program in spring, summer and fall to scour naturally occurring iron and manganese sediment out of the mains, and buildings on a section being flushed can see a morning of yellow, brown or reddish water and a pressure drop. I wrote that one up in the spring post, with the utility's numbers; the short version is that if your breakroom water went off-color for a day, check the flushing schedule before you call anyone.

What is constant: hardness

None of the above is the thing people complain about most. Madison's water is "very hard," 18 to 20 grains per gallon, from calcium and magnesium in the sandstone. That is the scale in the coffee maker, the white film on the kettle, and the mineral taste under everything else. It is the same in every season and at every well.

What this means for an office in Madison

The honest summary: your water is safe, and by municipal standards Madison's utility is unusually transparent. But the taste is not stable, and the reasons are local. Which well is on, how far the water travelled, how warm the pipes are, how much salt has reached your well, and whether a hydrant down the block got flushed this morning all change what comes out of the tap. None of them are things you can control from the breakroom.

A point-of-use system takes that variability out. Carbon removes whatever chlorine is left, reverse osmosis removes the hardness minerals and the chloride, and a sealed filter stack does not care which well came online in June. The water tastes the same in January and July because it is the same water by the time it reaches the glass.

If you run an office in Madison or the surrounding towns, the Madison bottleless water cooler page covers what the system is and what it costs, or get in touch and I will bring one over for a side-by-side taste test with what you have now.