Does Water Pressure Affect Your RO Purifier's Performance?

RO membranes require a minimum inlet pressure of 40 psi (2.8 bar) to operate effectively. Below this threshold, membrane rejection rates fall and output slows significantly. Most Nairobi households on upper floors experience inlet pressures below this minimum.

Why Pressure Matters in Reverse Osmosis

Reverse osmosis is a pressure-driven process. The applied pressure must overcome the osmotic pressure of the feed water, a force that opposes water movement across the membrane. For typical Kenyan tap water with a TDS of 200–400 mg/L, the osmotic pressure is approximately 10–20 psi. The system must exceed this threshold, plus overcome membrane resistance, to produce permeate (purified water).

The relationship between pressure and performance is not linear: below 40 psi, rejection rates fall disproportionately, meaning contaminants pass through the membrane at an increasing rate. A system running at 25 psi may be producing water with only 80–85% rejection of TDS, well below its rated performance.

Typical Pressure Conditions in Nairobi

Municipal supply pressure in Nairobi ranges widely by zone, supply period and floor level:

Solutions for Low-Pressure Households

• Booster pump: A small electric pump fitted to the RO inlet raises pressure to 60–80 psi regardless of incoming supply. This is the most common and reliable solution for upper-floor apartments.
• Gravity-feed design: Some systems are designed for gravity-feed from an elevated storage tank, operating at lower pressure with a larger membrane area to compensate.
• Elevated storage tank: Storing water at 3–4 metres above the RO system generates approximately 4–6 psi per metre of head, sufficient for ground-floor installations if storage is high enough.

When Pressure Is Too High

Excess pressure (above 80 psi / 5.5 bar) stresses membrane fibres and can cause premature failure. Buildings where pressure exceeds 80 psi, typically rare but possible during off-peak hours in low-lying zones, benefit from a pressure regulator fitted at the household inlet.

Q: How do I know what pressure I have?

A: A simple pressure gauge fitting available at any hardware store threads onto any standard tap connection and gives you a reading in psi or bar within seconds.

Optimised for Kenya's pressure conditions

iClear systems are configured for Nairobi's variable supply pressure. Find out more.