Total Dissolved Solids
TDS in water explained: what it measures, EPA secondary guideline (500 PPM), health significance, how to test with a TDS meter, and when treatment is needed.
TDS measures the total concentration of dissolved minerals, salts, and metals in water. It is not a health hazard at typical levels. The EPA secondary guideline is 500 PPM. High TDS affects taste, can indicate other contamination, and causes mineral buildup. Reverse osmosis is the most effective treatment for reducing TDS.
What is Total Dissolved Solids?
Total dissolved solids (TDS) is a measure of all dissolved inorganic and organic substances in water, including minerals (calcium, magnesium, sodium, potassium), salts (chlorides, sulfates, bicarbonates), metals, and small amounts of organic matter. TDS is not a single contaminant but an aggregate measurement of everything dissolved in the water. A TDS meter measures electrical conductivity as a proxy for total dissolved content.
Is Total Dissolved Solids Dangerous?
TDS itself is not a health risk at levels typically found in drinking water. Many of the dissolved minerals (calcium, magnesium, potassium) are essential nutrients. However, very high TDS can indicate the presence of specific harmful contaminants, and water with TDS above 1,000 PPM may have laxative effects. The health significance of TDS depends entirely on what substances make up the total.
How to Identify Total Dissolved Solids in Your Water
A handheld TDS meter ($10 to $25) provides instant readings. These meters are widely available and easy to use. Note that a TDS meter does not tell you what is dissolved in the water, only the total amount. A high reading warrants further testing to identify specific substances.
How Total Dissolved Solids Is Regulated
TDS is regulated only as an EPA secondary standard at 500 PPM. Secondary standards are non-enforceable aesthetic guidelines. Some states have adopted TDS standards for specific water sources.
| Standard | Limit | Notes |
|---|---|---|
| Secondary Standard | 500 PPM | Aesthetic guideline; not enforceable |
How to Remove Total Dissolved Solids
- Reverse Osmosis Recommended — 90% to 99% TDS removal · Single tap
- Distillation — 99%+ removal · Small batch
Total Dissolved Solids Levels in US Cities
| City | State | Level | Rating |
|---|---|---|---|
| Mesa | AZ | 600.0 PPM | Very High |
| El Paso | TX | 578.0 PPM | Very High |
| Glendale | AZ | 570.0 PPM | Very High |
| Yorkville | IL | 570.0 PPM | Very High |
| Washington | IL | 570.0 PPM | Very High |
| Hutchinson | KS | 570.0 PPM | Very High |
| Rio Rancho | NM | 564.0 PPM | Very High |
| Lake Havasu City | AZ | 558.0 PPM | Very High |
| Las Vegas | NV | 550.0 PPM | Very High |
| Salina | KS | 548.0 PPM | Very High |
| North Las Vegas | NV | 542.0 PPM | Very High |
| Wooster | OH | 540.0 PPM | Very High |
| Henderson | NV | 535.0 PPM | Very High |
| Tucson | AZ | 532.0 PPM | Very High |
| Maricopa | AZ | 532.0 PPM | Very High |
| Laredo | TX | 531.0 PPM | Very High |
| Plainfield | IL | 525.0 PPM | Very High |
| Howell | MI | 525.0 PPM | Very High |
| Dubuque | IA | 523.0 PPM | Very High |
| Bolingbrook | IL | 520.0 PPM | Very High |
Top 20 of 576 cities above 150 PPM in our database of 1000 cities. Look up your city.
Frequently Asked Questions
Is low TDS water unhealthy?
Does a water softener reduce TDS?
What is a good TDS level?
Sources
- EPA Secondary Drinking Water Standards — EPA secondary standard
- WHO TDS in Drinking-water Guidelines — Health effects