About 10 years ago I 'upgraded' my whole-house reverse-osmosis system. The old one had a big 1/2HP motor, a membrane that was near impossible to change (OMG, it was just impossible, I cannot fathom what they were thinking, needed a vice, a hammer, a chisel, 2 vice-grips, and a lot of patience). It was full of sound and fury, but ultimately signified nothing to (mis)quote the bard.
So I shelled out about $300 and got a watts premier. It ran off of city pressure, so no pump was needed. And you could change the carbon/membrane filters without thinking, easier than changing a lightbulb. And life was good, I just plumbed it in the same spot. My ice was clear, my tea tasted right, all was good in the world.
Well, in the last few winters the water main on my street has burst, and the city has dug and replaced, but also lowered the pressure. And I was seeing that I was not producing as much RO water as before. So my first thought was, new filters/membrane, maybe they are clogged. No, well, it improved a bit, but not much.
So my second thought was, well, input pressure is lower cuz the city put a reducer on our main, so I bought a booster pump. Its 24VAC and silent, unlike the old piston pump (its more like a fishtank pump).
Hmm, ok, same thing. Its maybe a bit better, but not great. I can't fill my kettle for iced-tea all at once. Hmm. And I'm all about the iced-tea.
OK, lets troubleshoot a bit more. An RO system is effectively a high-pressure side, run against a long membrane, which osmotically weeps pure water to the low pressure side. It then collects in a tank, and ... the tank. The tank is a ~20l collector with a rubber/neoprene balloon in it. And it is that balloon that gives the collected side pressure to run up to my 2nd floor etc. As the tank fills with water it compresses the balloon. When I open a tap, the balloon expands and pushes the water. So that balloon... has it leaked?
On the side of the tank is a standard air valve stem like you would see on a car or bike. A quick visit to the garage and the compressor and pressure gauge are obtained. I release the water from the tap, and find I have about 6psi present. What's the right pressure you ask? I dunno, couldn't be bothered to google, more must be better right? So I pumped it to 10. And now, its good as new! Air made it good.
So is it leaking? Well, maybe. If in a few weeks it goes back to the old state, I'm in for a new tank. Or another trip to the basement w/ the compressor.