TDS stands for total dissolved solids — the minerals and salts dissolved in your water, measured in milligrams per liter (mg/L). It's a count, not a safety grade: the EPA's 500 mg/L guideline is about taste, not health. Here's what a TDS reading really tells you, and what's typical for Iowa homes.
Every drop of water that comes out of your tap has spent time soaking through soil and rock, and it picked up souvenirs along the way. The U.S. Geological Survey puts it plainly: "Calcium, magnesium, sodium, potassium, bicarbonate, sulfate, chloride, nitrate, and silica typically make up most of the dissolved solids in water," and "all natural waters contain some dissolved solids" from contact with soils and rocks. Add all of those up and you get one number — TDS.
In Iowa, much of our groundwater has been marinating in limestone and dolomite for a very long time, which is why our water tends to arrive mineral-rich. That's geology, not a malfunction.
If you've seen someone on the internet dip a little pen-shaped meter into a glass of water and gasp at the number, you've met the TDS meter craze. Here's the honest scoop: a TDS meter gives you one combined total of everything dissolved in your water. That's it.
What it can't do is tell you what is dissolved. It can't tell harmless calcium from something you'd actually want to know about. Nitrate is a good example — Iowa State University Extension notes it's odorless and tasteless, so no meter, nose, or taste bud will flag it. Only a lab test identifies what's actually in your glass. If you're on a private well, free testing is available through your county under Iowa's Private Well Grants program, and you can read more about nitrates in Iowa water any time.
This is the part the viral videos skip. The EPA lists TDS under its secondary drinking water standards, which "are established as guidelines to assist public water systems in managing their drinking water for aesthetic considerations, such as taste, color, and odor." The EPA adds that these contaminants "are not considered to present a risk to human health" at the secondary level.
The flip side is true too. The Water Quality Association reviewed the research on very low-TDS water (like RO or distilled) and found that "worldwide, there are no agencies having scientific data to support that drinking water with low TDS will have adverse health effects." So a TDS number — high or low — is a mineral count, not a verdict. If a reading surprises you, the answer is a real test, not a panic.
The EPA's secondary standard for TDS is 500 mg/L, and the effects it lists are the everyday, around-the-house kind: "hardness; deposits; colored water; staining; salty taste." USGS agrees on the taste part — "concentrations greater than the recommended value for drinking water of 500 mg/L give water an unpleasantly salty taste."
Notice what's on that list: spots, film, and flavor. It's the same aesthetic territory as hard-water scale and chlorine taste — annoying, fixable, and not a reason to lose sleep.
Iowa's state geologists actually grade our groundwater by TDS. The Iowa DNR and Iowa Geological Survey's Bedrock Aquifers of Iowa map sorts the state into "Water Quality Regions based on Total Dissolved Solids: Good = < 500 mg/L; Fair = 500 - 1,000 mg/L; Poor = >1,000 mg/L." In other words, Iowa water spans the whole range depending on which aquifer your city or well taps — there's no single statewide "normal."
Some of our deepest, oldest water runs on the mineral-heavy end. A USGS review of Iowa groundwater found that "median concentrations for dissolved solids in the surficial, Dakota, and Jordan aquifers exceed secondary drinking-water standards." That Jordan aquifer may sound familiar if you live in Marion — the city draws about 63% of its water from 1,600-foot Jordan wells, which is part of why Marion's water is famously mineral-rich. Cedar Rapids, by contrast, pulls from shallow alluvial wells along the Cedar River and softens at the plant, so its dissolved mineral load looks very different a few miles away.
People often use "hard water" and "high TDS" interchangeably, but they're cousins, not twins. Hardness counts just two of the dissolved minerals — calcium and magnesium — while TDS counts everything on the list. USGS calls water very hard above 180 mg/L of those hardness minerals, and one grain per gallon (gpg) equals 17.1 mg/L.
Since calcium and magnesium are usually big contributors, hard water and higher TDS tend to travel together. Marion's unsoftened water runs 18-20 gpg — roughly 310-340 mg/L on the hardness scale alone — while Cedar Rapids taps land around 6.5-7 gpg after city softening. Curious where your town sits? We keep a running list in our Iowa water hardness by city guide.
If you want the number on the meter to drop, there's one workhorse: reverse osmosis. RO pushes water through a membrane fine enough to strain out dissolved minerals — systems certified to NSF/ANSI Standard 58 are tested to reduce TDS by at least 75%. The CDC also notes reverse osmosis reduces nitrate, which no amount of boiling can do.
An under-sink RO system treats the water you actually drink and cook with. We install tank-style RO for $800 and tankless for $900 — all-in, including installation, taxes, and lifetime parts coverage.
Carbon filters and pitchers. Activated carbon is genuinely great at what it does — the University of Nebraska-Lincoln notes it reduces chlorine, chloramines, and atrazine, which is why it fixes chlorine taste so well. But dissolved minerals aren't its job, so don't expect a carbon pitcher to move your TDS reading.
Water softeners. A softener swaps calcium and magnesium for sodium — UNL notes "sodium is added to water at a rate of about 8 mg/L for each grain per gallon (gpg) of hardness" removed. It's an ion trade, so the total dissolved load stays in the same ballpark even though your skin, laundry, and appliances feel the difference immediately. UNL is also clear that softening "does not remove bacteria, hydrogen sulfide, silt or sand, lead, nitrate, pesticides." Softeners solve scale and soap problems (here's what a softener costs in Eastern Iowa); RO solves TDS.
Boiling. Boiling is for germs. The CDC notes it does not remove chemicals like nitrate — so it's not a TDS strategy either.
TDS is a mineral count with a taste guideline attached — useful trivia, terrible lie detector. If you're curious what's really in your water, skip the $10 meter debate and get actual answers: we'll test your water for free, walk you through the results in plain English, and you can build an instant quote in about two minutes if anything's worth fixing. No pressure, no scare tactics — that's the kind way.
The EPA's secondary guideline is 500 mg/L — a taste-based recommendation, not a health rule. There's no minimum, either: the Water Quality Association reviewed U.S., Canadian, WHO, and European standards and found none set a lower limit, and no agency has data showing low-TDS water causes harm. Most people simply prefer how lower-TDS water tastes.
Not by itself. The EPA classes TDS as a secondary standard — an aesthetic guideline covering taste, deposits, and staining — and states these contaminants aren't considered a health risk at that level. But a meter can't rule anything out either, so if the number surprises you, a free water test that identifies what's actually dissolved is the sensible next step.
No. A softener trades calcium and magnesium for sodium — the University of Nebraska-Lincoln notes about 8 mg/L of sodium is added per grain of hardness removed — so the total stays in the same ballpark even though the water feels completely different. Softeners fix scale, spots, and soap problems; reverse osmosis is the tool that actually lowers TDS.
No. Boiling disinfects — it doesn't demineralize. The CDC notes boiling does not remove chemicals such as nitrate. If you want a lower TDS number at the kitchen tap, a reverse osmosis system certified to NSF/ANSI Standard 58 — tested to reduce TDS by at least 75% — is the practical fix.
Systems certified to NSF/ANSI Standard 58 are tested to reduce TDS by at least 75% — for water starting at 400 mg/L, that math works out to 100 mg/L or less in certification testing. We install tank-style RO for $800 and tankless for $900 — all-in with installation, taxes, and lifetime parts coverage — and both come with a free water test first.
Whole-home water softening, filtration, and reverse-osmosis drinking water — professionally installed and built to last a lifetime.
Serving Marion, Cedar Rapids & surrounding Linn County communities
Kind Water Co is a d/b/a of Zero Cap Investments LLC · 2258 Bison St, Apt B, Marion, IA 52302
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