Rainwater PPM Checker
Rain starts pure but picks up dust, roof grime, and pollution on the way down. Clean rainwater reads 5–20 PPM on a TDS meter; roof runoff can hit 100+. Enter your reading to see what you have got.
Calculator
Rainwater PPM Checker
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Rain starts pure but picks up dust, roof grime, and pollution on the way down. Clean rainwater reads 5–20 PPM on a TDS meter; roof runoff can hit 100+. Enter your reading to see what you have got.
How to use this calculator
- Enter TDS reading in PPM.
- Get a purity verdict.
- See first-flush guidance.
The formula
Purity bands based on typical harvested-rainwater TDS ranges.
What the units mean
PPM (parts per million) — one part of solute per million parts of the total mixture. The workhorse unit for trace concentrations in water, air, and food.
Worked example
First-flush diverter output: 12 PPM → clean enough for garden and laundry.
Quick reference
| Reading | Verdict |
|---|---|
| <20 PPM | Clean |
| 20–100 PPM | Usable non-potable |
| 100+ PPM | Check roof/contamination |
TDS meter readings.
Where you will actually use this
Rainwater harvesting is only as good as the water you actually collect.
- Rainwater harvesting
- Off-grid water
- Garden irrigation planning
Mistakes that give wrong answers
- Skipping the first-flush diverter
- Storing without filtration for drinking
Key takeaways
- Formula: Clean rainwater: typically 5–20 PPM TDS
- Remember: TDS meter readings.
- Watch out for: Skipping the first-flush diverter
- Next step: run your own numbers in the calculator above, then verify with a measurement — calculated values are only as good as the inputs.
Frequently asked questions
What is normal rainwater TDS?
5–20 PPM for clean rain.
Can I drink harvested rainwater?
Only with proper filtration and disinfection.