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(More customer reviews)I use this with my Watts RO system. The permeate pump has John Guest type connections, which is easy for connecting tubes. The connector size is 1/4 inch. Since my Watts system uses 3/8 inch tubes for the filtered water, I also bought 1/4 to 3/8 adapters (which will be included if you buy the permeate pump from Watts' site directly). The Watts manifold system has two 3/8" outputs to fork the filtered water to tank and faucet. I had to end one of them and add a 3/8 tee as a fork after the permeate pump. While I am writing this, I think I could have instead used a 3/8x3/8x1/4 tee between the manifold and the pump (no need to end an output and also save an adapter).
RO systems rely on water pressure difference on the two sides of membrane: the lower the pressure difference, the more wasted water. The often cited 4:1 waste water ratio is for when the tank is empty. As the tank fills, the pressure difference is smaller and more wasted water is generated and longer time is needed to produce the same amount of filtered water. This is why people who tested the ratio at home found higher ratios than the published one. In reality the waste ratio may be even higher as the tank is rarely empty before the system resumes to work again. This pump separates the tank from the membrane, making the pressure on the tank side of the membrane always low. As explained above, this will greatly reduce the amount of waste water.
When pressure difference on a membrane is low, the rejection rate (percentage of contaminants rejected) is also low, resulting in more TDS (total dissolved solids) in the filtered water. So, this pump will also increase rejection rate. High pressure difference also makes it faster to fill the tank, and a 24 GPD (gallons-per-day) membrane may be enough for a system that needed 50 GPD. In addition, the hydraulic pressure of the pump will push more water into the tank, resulting in a higher tank pressure when filled than without the pump.
An RO system has a shutoff valve, which shuts off the water when the pressure difference is low and reopens when the pressure difference increases to a certain level. This stops the system from wasting too much water. When this pump is used, it may render the shutoff valve useless. This is true especially for manifold systems like the Watts because the shutoff valve is built into the manifold and cannot see the tank pressure after the permeate pump is installed. As a result, the input water is never shut off. In this situation, the pump will act like a pseudo-shutoff valve and will shut off the system when tank pressure reaches a high level. But when the tank pressure is reduced a little (say by drawing a small cup of water), it immediately resumes to work. This increases the chance of TDS creep: even when the system stops, the membrane still sits in water, and the TDS on the tap water side will gradually creep through the membrane into the filtered water side. The more frequently the tap water is "refreshed" (as in the above scenario), the more TDS creeps into tank. I alleviated this problem by adding an auto shutoff valve externally between the tank line and the input water line. I used a regular shutoff valve (which shuts off at 60% pressure), but a 90% valve probably is better (see the comment by Waterdrinker).
The pump will generate a click sound every few seconds when it is working. This is normal and the sound is nothing compared to the hissing noise from the air gap of the RO system.
Compared to not using the pump, I probably save 4-5 gallons water for each gallon of filtered water. We use about 3 gallons per day for cooking and drinking. So our annual saving is about 5000 gallons, or about 15-20 bucks a year.
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