TDS — total dissolved solids — is the amount of minerals, salts and metals dissolved in water, measured in milligrams per litre (mg/L) or parts per million (ppm). It is the single most useful number for deciding whether you need an RO purifier.
What does BIS say?
The Indian drinking-water standard, BIS IS 10500, sets an acceptable limit of 500 mg/L for TDS. In the absence of an alternative source, it allows up to 2000 mg/L as the permissible limit. Water within the acceptable limit is generally considered fine for drinking from a TDS point of view.
A practical guide
| TDS (mg/L) | What it means |
|---|---|
| Below 50 | Very low — can taste flat; minerals may be lacking |
| 50 – 150 | Excellent taste for most people |
| 150 – 300 | Good |
| 300 – 500 | Acceptable as per BIS |
| Above 500 | RO purification recommended |
Do I need RO or UV?
If your input TDS is below about 200–300 mg/L (typical of many municipal supplies), a UV or UF purifier may be enough. If you use borewell or tanker water with high TDS — common in parts of Delhi, Hyderabad and the outer areas of many cities — RO is the right choice. Read RO vs UV vs UF.
Low TDS is not always better
A badly set RO can bring TDS down to 10–20 mg/L. Such water tastes flat. Most purifiers have a TDS controller or mineral cartridge to bring it into a pleasant range. Our technicians set this for your water during every RO service.
Want your water checked? A free TDS test is included with every visit — book now.