A good TDS reading for drinking water falls between 300 and 500 parts per million (ppm). This range provides enough dissolved minerals for pleasant taste without the hardness, staining, or salty flavor that comes with higher levels. The EPA sets a secondary guideline at 500 ppm, above which water may taste noticeably off or leave deposits on fixtures.
TDS Ranges and What They Mean
TDS stands for total dissolved solids, a measure of everything dissolved in your water: calcium, magnesium, sodium, potassium, zinc, and other minerals and salts. A higher number means more dissolved material. Here’s how the ranges break down in practical terms:
- Below 50 ppm: Very low mineral content. Water may taste flat or “empty.” Long-term consumption of heavily demineralized water raises concerns about missing out on minerals your body needs.
- 50 to 250 ppm: Low to moderate. Drinkable and clean-tasting, but potentially lacking beneficial minerals like calcium and magnesium.
- 300 to 500 ppm: The sweet spot. Water at this level typically has a balanced mineral profile and tastes neither flat nor heavy.
- 600 to 900 ppm: Noticeable mineral taste. You may see scale buildup in kettles and on faucets. A filtration system like reverse osmosis can bring this down.
- 1,000 to 2,000 ppm: Not recommended for regular drinking. Likely has a strong mineral or salty taste.
- Above 2,000 ppm: Considered unsafe. Standard household filters cannot adequately handle this level.
Why Very Low TDS Isn’t Ideal Either
If you use a reverse osmosis (RO) system or buy certain brands of purified water, your TDS might sit well below 50 ppm. While that sounds “pure,” it comes with trade-offs. Drinking water is actually a meaningful source of calcium and magnesium, and even people with otherwise good diets may not fully compensate for the absence of these minerals in their water.
Demineralized water also pulls minerals out of food during cooking. Research published in the Medical Journal, Armed Forces India found that boiling vegetables or meat in very low-TDS water can leach up to 60% of their calcium and magnesium content, with losses reaching 70% or more for trace minerals like manganese and cobalt. Over the long term, regularly drinking and cooking with heavily demineralized water has been linked to higher risk of fractures in children, certain pregnancy complications, and cardiovascular concerns. Magnesium in drinking water appears to be a key protective factor for heart health.
If your RO system drops your water below 50 ppm, consider a remineralization filter that adds calcium and magnesium back in. Many newer RO systems include one as a final stage.
What High TDS Water Does to Your Body
A TDS reading above 500 ppm doesn’t automatically mean your water is dangerous, but it does mean you should pay attention to what’s driving the number up. The most common culprits are calcium and magnesium, which make water “hard.” High levels of these minerals cause the scale you see on showerheads and inside pipes, and they can give water a chalky or bitter taste.
When magnesium and sulfate are both present at high concentrations (around 250 mg/L each), the combination can have a laxative effect. More than three-quarters of kidney stones are made of calcium salts, though the research on whether hard water actually increases stone risk is mixed. Some studies find a weak connection; others find none at all. For people who’ve already had calcium kidney stones, softer water may be preferable as a precaution.
The real concern with high TDS is when the dissolved solids include harmful contaminants rather than just common minerals. A TDS meter can’t tell you what’s in your water, only how much total dissolved material is present. Lead, arsenic, or nitrates all contribute to TDS the same way calcium does. If your reading is unexpectedly high, a lab test from your local water utility or a certified testing service will break down exactly what’s dissolved in it.
How TDS Meters Actually Work
Handheld TDS meters are inexpensive and easy to use, but they don’t directly measure dissolved solids. They measure electrical conductivity, the ability of your water to conduct a small current, and then multiply that reading by a conversion factor to estimate TDS. Pure water barely conducts electricity. The more dissolved minerals and salts present, the more conductive the water becomes.
The conversion factor isn’t fixed. At low conductivity levels, the meter multiplies by about 0.50. At higher levels, the factor climbs to 0.65 or above. This means TDS meters give a reasonable estimate for typical tap water but can be less accurate at extremes. They also can’t distinguish between harmless calcium and something like lead, so treat the reading as a general indicator of water quality rather than a definitive safety test.
TDS Is Not the Same as Hardness
People often confuse TDS with water hardness, but they measure different things. Hardness specifically tracks calcium, magnesium, and other minerals that carry a double positive charge. TDS includes everything dissolved in the water, including sodium, potassium, chloride, and other ions that don’t contribute to hardness at all. As a rough shortcut, dividing your TDS reading by 10 gives you an approximate hardness value, but it’s only an estimate with a margin of error of a few degrees.
This distinction matters if you’re deciding whether to buy a water softener versus an RO system. A softener swaps calcium and magnesium for sodium, which reduces hardness and scale but may not lower your TDS reading much (and can even raise it slightly). An RO system removes the vast majority of all dissolved solids. According to FDA data, a standard RO system rejects 90% to 95% of TDS. Feed water at 300 ppm would come out between 15 and 30 ppm.
Checking Your Own Water
If you’re on a public water system, your utility publishes an annual water quality report (sometimes called a Consumer Confidence Report) that includes TDS along with dozens of other measurements. You can usually find it on your utility’s website. For well water, you’ll need to test it yourself since no one monitors it for you.
A basic TDS meter costs $10 to $20 and gives you a quick reading in seconds. Dip the probes in a glass of water, wait for the number to stabilize, and you have your ppm. Test at the tap you drink from most, since readings can vary depending on your plumbing and whether you have any inline filters. If your reading lands between 300 and 500 ppm, your water is in the ideal range for both taste and mineral content. If it’s significantly above or below that window, filtration or remineralization can bring it into balance.