The membrane is the heart of any RO system and the part customers ask about most. You do not need a chemistry degree to sell and service it well, but a clear mental model helps you choose the right element and explain it with confidence.
Reverse Osmosis: The Basic Mechanism
In nature, osmosis moves water from a low-concentration side to a high-concentration side through a semi-permeable layer. Reverse osmosis does the opposite: a pump applies pressure to push water against that natural flow, through a membrane so fine that water molecules pass while dissolved salts and contaminants are left behind.
That membrane filters down to around 0.0001 micron. At that level it blocks dissolved solids, heavy metals, and most bacteria and viruses, which is why RO handles high-TDS water that UV or UF alone cannot.
The pressure for that push comes from the RO booster pump. Weak pressure means weak rejection and slow output, so the pump and the membrane work as a pair.
GPD Ratings: 80 GPD vs 100 GPD
GPD means Gallons Per Day, the membrane's rated output under test conditions. It is a capacity guide, not a promise of tap speed.
- 80 GPD: the workhorse for most Indian homes. Reliable recovery and good rejection on normal to hard water.
- 100 GPD: more output for larger families, or where input pressure runs low and you need headroom.
Real output is always below the lab figure because feed pressure, temperature, and TDS all affect it. Both the Eco Series and High TDS Series come in 80 and 100 GPD so you can match the home.
Membrane Rejection Rate: What It Measures
Rejection rate is the percentage of dissolved solids the membrane removes:
Rejection % = (Input TDS minus Output TDS) / Input TDS x 100
A healthy domestic membrane holds high rejection across its life. Watch the trend, not a single reading. If a membrane that gave a large TDS drop at install is now letting far more through, rejection has fallen and performance is degrading. Match the membrane to the feed water using the TDS guide so rejection stays where it should.
Signs a Membrane Needs Replacing
Tell customers what to watch for, and check these on a service visit:
- Output TDS creeping up over weeks or months.
- Noticeably slower fill of the storage tank.
- Taste or odour returning even with fresh pre-filters.
- Age: most domestic membranes run about 2 to 3 years, less on high-TDS water.
Always rule out clogged pre-filters and a weak pump first. A tired sediment filter or failing pump often masquerades as a dead membrane.
FreshDrop Eco Series vs High TDS Series: Which to Choose
- Eco Series: your default for municipal and moderately hard water. High flow, long life, strong value for volume jobs.
- High TDS Series: built for borewell and high-mineral input where a standard element would struggle to hold rejection.
When in doubt, decide on the input TDS reading, not the price.
Want both series in 80 and 100 GPD at wholesale rates, with GST billing and pan-India shipping? Contact Nitesh Enterprise for a quote.