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TDS and Hardness Checker
Type in the reading from a TDS meter, a test strip or a lab report and see what it means for taste, scale and your appliances, and what would fix it.
What is TDS in water?
TDS stands for total dissolved solids: everything dissolved in the water that would be left behind if it evaporated, mostly salts and minerals such as calcium, magnesium, sodium, chloride, bicarbonate and sulphate. It is measured in milligrams per litre (mg/L), which for drinking water is the same as parts per million (ppm).
A TDS meter measures how well the water conducts electricity and converts that to an estimate of TDS. That makes it a quick, cheap check on taste and on how well a reverse osmosis system is working, but not on safety.
TDS chart for drinking water
| TDS (mg/L or ppm) | Taste rating | What it usually means |
|---|---|---|
| Below 300 | Excellent | Typical of good municipal water, rainwater and RO water |
| 300 to 600 | Good | Fine for drinking; minerals may be noticeable in tea or coffee |
| 600 to 900 | Fair | A mineral or salty taste many people notice |
| 900 to 1 200 | Poor | Distinct taste, more scale; worth treating for drinking |
| Above 1 200 | Unacceptable | Above the SANS 241 aesthetic limit of 1 200 mg/L |
Taste ratings from the World Health Organization's background document on total dissolved solids. The SANS 241 limits for TDS (1 200 mg/L) and conductivity (170 mS/m) are aesthetic limits in the 2015 edition of the standard.
What is hard water?
Hard water carries more dissolved calcium and magnesium. It is not a health risk, but it leaves scale on kettles, shower glass and taps, coats the element in your geyser and makes soap lather less easily. Hardness is usually reported as mg/L of calcium carbonate (CaCO₃).
| Class | mg/L as CaCO₃ | °dH | gpg |
|---|---|---|---|
| Soft | 0 to 60 | 0 to 3.4 | 0 to 3.5 |
| Moderately hard | 61 to 120 | 3.4 to 6.7 | 3.5 to 7 |
| Hard | 121 to 180 | 6.7 to 10 | 7 to 10.5 |
| Very hard | Above 180 | Above 10 | Above 10.5 |
Hardness classes from the US Geological Survey. 1 °dH is 17.8 mg/L and 1 grain per gallon is 17.1 mg/L as CaCO₃. The WHO notes that scale tends to form above about 200 mg/L, and that very soft water can be more corrosive to pipes.
Fixing high TDS or hard water
- High TDS in drinking water: reverse osmosis at the kitchen tap lowers dissolved solids substantially. Carbon and sediment filters do not.
- Hard water and scale: a water softener on the main supply protects the geyser, taps and appliances.
- Chlorine taste on good-TDS water: a carbon filter deals with taste and smell without changing the minerals.
- Borehole water: start with a laboratory test, because the fix depends on what is dissolved. Our borehole water treatment guide explains the order of stages.
FAQs
TDS and hardness questions
What TDS level is good for drinking water?
Taste panels used by the World Health Organization rate water below 300 mg/L as excellent, 300 to 600 mg/L as good, 600 to 900 mg/L as fair, 900 to 1 200 mg/L as poor and above 1 200 mg/L as unacceptable. South Africa's drinking water standard, SANS 241, sets an aesthetic limit of 1 200 mg/L. These are taste and appearance limits, not health limits.
Is high TDS in water harmful?
TDS on its own is mostly about taste, scale and how hard water is on appliances. What matters for health is what the dissolved solids are, such as nitrate, fluoride or metals, and a TDS meter cannot tell them apart. If your reading is high, especially on borehole water, a laboratory test shows what is in it.
Does a water filter reduce TDS?
Most do not. Sediment and carbon filters improve clarity, taste and smell but leave dissolved salts and hardness in the water, so a TDS meter reads much the same before and after. Reverse osmosis is the treatment that lowers TDS substantially.
Is Cape Town tap water hard?
It depends on the source. The City of Cape Town notes that groundwater is usually harder than surface water, and has quoted around 40 to 50 mg/L for the Somerset West supply, which is soft. A test strip or a lab test tells you what comes out of your own tap.
What does ppm mean on a TDS meter?
Parts per million. For drinking water, 1 ppm is the same as 1 mg/L, so a reading of 250 ppm is 250 mg/L of dissolved solids. Most handheld meters measure conductivity and convert it to TDS with a fixed factor, so treat the result as a close estimate.
Related guides
Reverse Osmosis vs UV: Which Water Filter Do You Need?
Reverse osmosis vs UV explained: what each removes, what each needs to work, whether RO water is healthy, and which suits municipal, borehole or rainwater.
Read Guide
Is Tap Water Safe to Drink in South Africa? (Cape Town Included)
Can you drink tap water in Cape Town? What SANS 241 and the latest Blue Drop results show for South Africa, why quality varies and when a filter helps.
Read Guide
Is Borehole Water Safe to Drink? How to Know for Sure
Is borehole water safe to drink? Sometimes, but only a SANS 241 lab test can tell you. What can be in it, how to test it and what to do while you wait.
Read Guide
Not sure what your reading means for your home?
Send us the reading and your water source. We will tell you whether it needs treating and what would fix it.