Total Dissolved Solids (TDS)
TDS·Affects kidneys
EPA secondary standard 500 mg/L (cosmetic, not enforceable). TDS is the sum of every dissolved mineral in your water: calcium, magnesium, sodium, sulfate, bicarbonate, and more. High TDS affects taste and accelerates scale buildup but is not a direct health concern.
TDS
EPA limit
500 mg/L (SMCL)
Most at risk
Anyone who notices a salty, mineral, or flat taste in their water
Found in
City water · Well water
AquaOx filters
Pair with ROPair with under-sink RO
What it does to you
Health effects
TDS itself is not a health hazard. It is a bulk measurement of dissolved mineral content, and the individual minerals contributing to it (calcium, magnesium, sodium, sulfate, bicarbonate, chloride) are mostly benign at typical concentrations. The EPA secondary standard of 500 mg/L is set for taste and appliance impact, not toxicity.
The health question depends entirely on what is dissolved. A 1,000 mg/L TDS reading dominated by calcium and bicarbonate is harmless and arguably beneficial. The same reading dominated by sodium matters for people on low-sodium diets, and the same reading dominated by sulfate becomes a laxative concern. TDS is a screening number, not a diagnostic one.
Very low TDS (below 50 mg/L) is also not a health issue, despite occasional online claims. Distilled and RO water are safe to drink; the body gets its minerals primarily from food, not water.
Where it comes from
How it gets into your water
TDS comes from every source that puts dissolved minerals into water. Groundwater picks it up from the rock and soil it moves through, surface water picks it up from runoff and tributary streams, and treated city water picks up additional dissolved solids from disinfection chemicals and pipe corrosion.
Arid regions tend to have higher TDS because evaporation concentrates dissolved minerals in surface water and shallow aquifers. The Southwest, Plains, and parts of Florida regularly see TDS above 500 mg/L from purely natural causes. Coastal aquifers can run high from saltwater intrusion.
Mineral dissolution
Groundwater contact with soluble rock formations
Runoff and erosion
Soil minerals wash into surface water sources
Treatment additives
Disinfectants and coagulants raise dissolved solids
Saltwater intrusion
Coastal aquifers can be contaminated by seawater
Find out for yourself
Is it in your water?
TDS is the easiest contaminant to measure at home. A $15 handheld TDS meter from any hardware store reads it in seconds. Anything above 500 mg/L is above the EPA secondary standard; readings of 50 to 300 are common in well-treated city water; readings of 800 to 1,500 are common in well water across arid regions.
Your annual CCR will list TDS if the utility tests for it, though many do not because it is a secondary standard. For well water, a basic inorganics panel breaks the TDS down into its component minerals, which is the actually-useful number for deciding what (if anything) to treat.
The fix
How AquaOx filters it
TDS is not filtered by activated carbon, KDF, or any media in a standard AquaOx whole-house system. Carbon and KDF target organic compounds, chlorine, and specific reactive metals. They do not pull dissolved salts and minerals out of solution.
The only practical way to reduce TDS in residential water is reverse osmosis or distillation. We recommend an under-sink RO unit on the kitchen tap for drinking and cooking water, paired with the whole-house AquaOx for everything else. RO drops TDS by 90 to 99% depending on the membrane and feed-water quality. For homes that want low-TDS water on every fixture, whole-house RO is possible but expensive and high-maintenance.