You have probably seen "TDS" on your RO purifier or water bill, but what does it really mean β and what is the best TDS level for drinking water? Getting this right matters for both taste and health. Here is a simple, practical guide.
What Is TDS?
TDS stands for Total Dissolved Solids β the total amount of dissolved minerals, salts and metals in your water, measured in parts per million (ppm) or milligrams per litre (mg/L). Some of these, like calcium and magnesium, are healthy minerals. Others, like lead, arsenic and excess nitrates, are harmful. TDS on its own tells you the quantity of dissolved substances, not exactly which ones β but it is a useful everyday indicator of water quality.
The Ideal TDS Range for Drinking Water
As a general guide widely used in India:
- Below 50 ppm β too low. Water can taste flat and lacks healthy minerals.
- 50 to 150 ppm β good, especially if you want a light, clean taste.
- 150 to 300 ppm β generally considered the ideal range for taste and mineral balance.
- 300 to 500 ppm β acceptable but on the higher side.
- Above 500 ppm β high; RO purification is recommended.
- Above 1,000 ppm β not suitable for drinking without proper treatment.
For most people, water in the 150β300 ppm range offers the best balance of taste and beneficial minerals.
Why Very Low TDS Is Not Ideal
It is a myth that "lower TDS is always better." Water with extremely low TDS (below 50 ppm) tastes flat and is stripped of healthy minerals your body benefits from. This is exactly why many modern RO purifiers include a TDS controller or mineraliser β it adds back essential minerals so your water is both safe and healthy. If your RO water tests very low, ask a technician to adjust the TDS controller or fit a mineraliser.
How to Check Your Water's TDS at Home
Checking TDS is quick and cheap with a handheld TDS meter:
- Switch on the meter and dip it into a glass of the water you want to test.
- Wait a few seconds for the reading to stabilise.
- Note the ppm value shown.
- Test both your input (tap) water and your purified RO water to see the difference.
Comparing input and output TDS is also the best way to judge your membrane's health β if the output TDS keeps rising toward the input value, your membrane is wearing out.
When RO Is Actually Needed
If your input water TDS is above 500 ppm, an RO purifier is the reliable way to bring it into a safe, tasty range. If your input TDS is already low (under 200 ppm) and the water is microbiologically safe, a UV or UF purifier may be enough β an RO could strip out too many minerals. A quick water test helps you choose the right purifier instead of guessing.
Keep an Eye on TDS Over Time
Test your purified water every couple of months. A stable reading in the healthy range means your system is working well. A steadily rising reading is your cue to book a service and check the membrane.
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