Every RO sale starts with one number: TDS. Get it right and you fit the correct membrane the first time. Get it wrong and the customer calls you back about taste, low output, or a membrane that fails early. This guide keeps it practical for dealers and technicians on the ground.
TDS and Drinking Water: What the Numbers Mean
TDS stands for Total Dissolved Solids. It is the combined weight of everything dissolved in the water, measured in parts per million (ppm) or mg/L: calcium, magnesium, sodium, chlorides, sulphates, nitrates, and traces of metals.
A TDS meter does not tell you what is dissolved, only how much. Two samples at 600 ppm can taste and behave very differently. So treat TDS as your first reading, not your only one, especially where the source is borewell or industrial-area supply.
Safe TDS Levels for Drinking Water in India
As a working reference for Indian homes:
- Up to 300 ppm: considered good drinking water.
- 300 to 600 ppm: acceptable; most municipal supply sits here.
- 600 to 900 ppm: hard water; RO is genuinely needed.
- 900 to 2000 ppm and above: high TDS; common with borewells and in many parts of Gujarat, Rajasthan, and Telangana.
The Bureau of Indian Standards puts the acceptable limit at 500 ppm and the permissible limit (with no better source) at 2000 ppm. Below roughly 150 ppm you usually do not need RO at all; a UV or UF system is enough, and over-purifying flat, mineral-poor water is a common mistake.
TDS and Your Choice of RO Membrane
Membranes are built for a feed-water range. Push a standard membrane onto high-TDS borewell water and you get low recovery, frequent flushing, and a short service life. The TDS reading is what points you to the right element.
For everyday municipal and moderately hard water, a balanced, high-flow element like the FreshDrop Eco Series RO membrane is the sensible default. For tough borewell or high-mineral input, step up to the FreshDrop High TDS Series membrane, which is rated to hold rejection on harder feed water.
High TDS vs Normal TDS: Which Membrane to Stock
Stock for the water in your area, not for a catalogue:
- Municipal / mixed areas: keep Eco Series moving as your volume line.
- Borewell / high-TDS belts: make High TDS Series your default and keep Eco Series for the lighter jobs.
- Carry both 80 GPD and 100 GPD. 80 GPD suits most homes; 100 GPD helps where input pressure is low or the family is large.
If you want the mechanics behind rejection rate and GPD before you decide, read how an RO membrane works.
Testing TDS at a Customer Site
A clean site test avoids returns:
- Run the tap for 30 seconds before sampling so you read the supply, not standing pipe water.
- Measure input TDS first and note it on the job sheet.
- After installation, measure output TDS. For a healthy membrane expect a large drop, typically to well under 100 ppm depending on input.
- Calculate rejection: (input minus output) divided by input. A sharp fall in rejection over time is your cue that the membrane is near end of life.
Log the input number for every customer. Over a few months it tells you exactly which membrane to stock more of.
Stocking RO membranes for a high-TDS area, or want bulk pricing on Eco and High TDS Series? Contact Nitesh Enterprise for a wholesale quote.