TDS Water Quality Calculator
TDS ppm, taste grade, and EPA check from EC.
What it does
TDS turns invisible water load into one number: the milligrams of dissolved minerals per liter. Taste dulls, spots bloom, and heaters scale as that number climbs.
The tool above takes EC conductivity in uS/cm. It returns estimated ppm, the taste grade, and the EPA 500 check.
The default 500 uS/cm reads about 320 ppm, Good and under the guideline. The hard case of 1000 reads 640, Fair and over.
EPA secondary standards draw the 500 line for taste and staining without health enforcement. WHO palatability guidance bands the same climb from excellent under 300 to unacceptable past 1200.
Meters screen; labs diagnose. The 0.64 conversion shifts with the actual ion mix, so odd or important readings deserve full analysis before buying treatment.
How to use
- Type EC in uS/cm.
- Read ppm first.
- Read the taste grade beside it.
- Read the EPA check last.
- Confirm odd readings with a lab.
- Size treatment to the ions.
Formula
- EC
- Conductivity in microsiemens per cm.
- TDS
- Dissolved solids in mg/L, about.
- grade
- WHO taste bands by ppm.
EPA secondary drinking water standards set 500 mg/L TDS for taste and staining as guidance rather than enforceable health limits. WHO drinking water guidance grades palatability across the same 300/600/900/1200 bands. The 0.64 factor is the common meter conversion; true factors run 0.5 to 0.7 by ion mix.
Worked example
Example: 500 uS/cm tap water
Default: 500 uS/cm EC.
- Meter: 500 uS/cm EC.
- TDS: 500 x 0.64 = 320 ppm.
- Grade: 300 to 600 reads Good.
- EPA: 320 sits under the 500 guideline.
- Check: 320/500 = 64% of the line.
- Tool shows 320 ppm, Good, Under EPA 500 guideline.
Reference table
| ppm | Grade | EPA |
|---|---|---|
| Under 300 | Excellent | Under |
| 300 to 600 | Good | Under to 500 |
| 600 to 900 | Fair | Over |
| 900 to 1200 | Poor | Over |
| Over 1200 | Unacceptable | Over |
Limits
- Estimate; ions shift the factor.
- Taste grades, not health verdicts.
- Single grab, not system survey.
- Softeners raise readings by design.
Common mistakes
- Reading TDS as a health failure.
- Chasing zero with over treatment.
- Trusting uncalibrated meters.
- Ignoring temperature effects.
- Treating symptoms, not ions.
Try it yourself
Quick checks. Answers sit tucked under each question.
EC 1000?
640 ppm, Fair, over the EPA 500 guideline.
EC 100?
64 ppm, Excellent, under the guideline.
EC minus 5?
Negative conductivity is unphysical: enter EC from 0 up.
Questions
EC to TDS?
Multiply EC by about 0.64. Meters with TDS mode do exactly this inside.
Taste grades?
Under 300 excellent, 300 to 600 good, 600 to 900 fair, 900 to 1200 poor, over 1200 unacceptable for taste.
EPA 500 meaning?
500 mg/L secondary standard: taste, staining, and scaling guidance, not a health enforceable line.
Meters enough?
Yes for screening. True composition needs lab ions, since different salts conduct differently.
Softened water reads high?
Softeners swap hardness for sodium, often raising TDS. Treat the cause the test names.
Lower TDS how?
Reverse osmosis or distillation for dissolved load; carbon polishes taste and chlorine only.