Total Dissolved Solids (TDS) in Well Water
What it is
TDS is the total amount of minerals, salts and other substances dissolved in water. EPA includes it in the yearly private well test.
Guideline
EPA's secondary level and Health Canada's aesthetic objective are both 500 mg/L. High TDS mostly affects taste and scaling.
If it's high
Ask the lab which ions are high: hardness, sodium, chloride or sulfate. A sudden rise can point to road salt, a nearby spill, or a well problem.
Sources
- EPA: Protect your home's water
- EPA: Secondary drinking water standards
- Health Canada: Guidelines for Canadian Drinking Water Quality, summary table
Questions
Is high TDS dangerous?
TDS itself is an aesthetic measure. What matters is which substances make it up.
Free well water safety checklist
15 family-friendly steps based on CDC and EPA guidance. Print it, keep it on the fridge, and know when to call a certified lab.
More guides
- Flood Protection for Well Owners: Before, During and After a FloodRaise and seal the wellhead, know your pump shutoff, then disinfect and test with a certified lab after any flood.
- PFAS “Forever Chemicals” in Private Wells: Why You Should TestFederal PFAS rules protect public water systems — not private wells. Here’s what “forever chemicals” mean for well owners and how to get tested.
- Nitrates in Well Water and Blue Baby Syndrome: Who Must TestNitrate in well water can cause blue baby syndrome in infants. Learn who is at risk, when to test, and how to find a certified lab.
- Arsenic in Private Well Water: The Invisible Risk UndergroundArsenic in groundwater is often naturally occurring and invisible. USGS research shows millions of private-well users may be above the EPA drinking-water standard.