The Effect of Water Temperature on a Reverse Osmosis Membrane

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The reverse osmosis membrane is a core component of any RO water purification system.

But it’s also a delicate component that can be affected by numerous factors, including input water temperature.

If you’re worried about the effects of temperature on your reverse osmosis membrane, keep reading. This article explains how temperature affects the RO membrane and what you can do to improve your membrane’s flow rate and contaminant reduction.

Key Takeaways

  • Water temperature affects RO membrane flow rate and salt rejection rate.
  • The flow rate increases with warmer water, while the salt rejection rate decreases with higher temperature (meaning fewer contaminants are removed).

The Effect of Water Temperature on a Reverse Osmosis Membrane

Water temperature affects the flow rate and salt rejection rate of any RO membrane.

Flow Rate

A high water temperature increases the flow rate through a reverse osmosis membrane, while a low temperature lowers the flow rate.

The science behind this is straightforward; cold water is more viscous (thicker) than warm water, so it flows through an RO membrane slower. Warm water is much thinner (or less viscous), so it flows faster.

Putting things in perspective, for every degree Fahrenheit drop in water temperature, the product flow rate goes down by around 3%, and for every °F rise in water temperature, the product flow rate goes up by roughly 3%.

Salt Rejection

Experiments have shown that water temperature also affects an RO membrane’s salt rejection rate.

When the water temperature increases, there’s an increase in salt permeability. This means that when the water is warmer, more salt escapes through the RO membrane, and fewer contaminants are removed.

blue reverse osmosis membrane

Temperature Correction Factor (TCF)

Manufacturers typically specify the flow rates you should expect from their reverse osmosis systems and membranes. But these flow rates were determined under strict lab conditions, and they assume that your feed water has an optimal temperature of 77 °F (25°C).

In reality, your water may have a different temperature. To determine membrane permeate rate or flow rate at any temperature, multiply the rated flow of the RO membrane by the TCF we’ve listed in the table below.

Note: All RO membranes have different manufacturing processes and show differences in chemistry, so correction factors vary. As such, use the table below as a rough guide for temperature correction factors and not as definitive.

Water Temp °C Water Temp °F TCF
5 41 0.42
5.5 41.9 0.43
6 42.8 0.45
6.5 43.7 0.47
7 44.6 0.49
7.5 45.5 0.51
8 46.4 0.52
8.5 47.3 0.53
9 48.2 0.55
9.5 49.1 0.56
10 50 0.58
10.5 50.9 0.60
11 51.8 0.61
11.5 52.7 0.62
12 53.6 0.63
12.5 54.5 0.64
13 55.4 0.65
13.5 56.3 0.67
14 57.2 0.68
14.5 58.1 0.69
15 59 0.70
15.5 59.9 0.72
16 60.8 0.73
16.5 61.7 0.74
17 62.6 0.76
17.5 63.5 0.77
18 64.4 0.78
18.5 65.3 0.80
19 66.2 0.81
19.5 67.1 0.83
20 68 0.84
20.5 68.9 0.86
21 69.8 0.87
21.5 70.7 0.89
22 71.6 0.90
22.5 72.5 0.92
23 73.4 0.93
23.5 74.3 0.95
24 75.2 0.97
24.5 76.1 0.98
25 77 1.00
25.5 77.9 1.02
26 78.8 1.03
26.5 79.7 1.04
27 80.6 1.06
27.5 81.5 1.08
28 82.4 1.09
28.5 83.3 1.11
29 84.2 1.12
29.5 85.1 1.14
30 86 1.16

What Can You Do to Increase Your Membrane’s Flow Rate? Raise Water Temperature!

Raising your input water temperature is one of the ways to increase your RO membrane’s flow rate.

To achieve this, you could coil up some feedwater tubing and let it rise to room temperature, or wrap the feedwater tubing around a warm object (like a water heater).

Note: Raising the temperature above 95 °F (35°C) can lead to membrane damage. This method is not guaranteed to improve your membrane life, so it’s best to confirm with the manufacturer before attempting it.

If you have any questions about the effect of temperature on a reverse osmosis membrane please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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Gene

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