I installed my RO system a year ago and it still works great, as is evident from the low TDS readings and no practically zero hardness (checked using test strips). It's connected to a drinking water dispenser, through a remineralization filter. I also use it to make RPavlis water, where I dispense the water from a separate hose, bypassing the remineralization filter.

I don't see any urgent need to replace any of the filters, but I'd like to also check that bacteria is not an issue. For this I purchased a test kit by a brand called Health Metric. It bought the single test pack and am wondering what should I test - water from the bypass hose, or from the drinking water dispenser. Thoughts?

Thanks!

The typical reverse osmosis filter has a pore size of approximately 0.0001 micron. This makes them very effective at removing protozoa, bacteria, viruses and common chemical contaminants. However, most manufacturers do not sell or warrant their systems to remove 100% of anything. Many specifically state that potable source water must be used. If you test your product water (from the spigot), chances are it will be free of bacteria. If you test the bypass water, I'd expect to see a greater concentration of any of the aforementioned contaminants than is present in the source water. When we moved into our cottage, the water supplied to the development was on boil advisory; the developer delivered jugs of RO water for drinking. Eventually, we told him to discontinue delivery and we drank water from our RO system with no ill effects. We're still here and healthy...YMMV

Interesting feedback, thank you. Can you explain why the water that goes through the bypass hose is more likely to have bacteria than that from the water dispenser? Both go through the same RO system, it's just that one is directed to a hose, while the other to a remineralization filter and an under-sink chiller.

The two water flows are different. The product water flows through the membrane, leaving behind impurities on the surface of the membrane. The waste water flows over the membrane, rinsing off the accumulated impurities. If it were not for this waste water flow, the membrane would quickly become clogged and stop working.

The problem of bacterial overgrowth is mainly in standard membrane/column filtration systems, where bacteria and other microscopic life forms can hang out and prosper. They typically will prevent bacteria from passing across the membrane, but the input side of the membrane and filter tank will essentially turn into a Petri dish unless measures are taken to prevent that. The way RO systems work, with constant flushing to clear the membrane, makes it less likely that the RO tank will become an incubator, but doesn't entirely eliminate the problem. There are several things that can be done, including UV treatment (also used with non-RO filtration systems) to minimize the risk.

Nunas wrote:The two water flows are different. The product water flows through the membrane, leaving behind impurities on the surface of the membrane. The waste water flows over the membrane, rinsing off the accumulated impurities. If it were not for this waste water flow, the membrane would quickly become clogged and stop working.

I'm not using the waste water. Both the drinking water and the water I use for espresso are from the tank (i.e. after the membrane). I may have used the term "bypass" incorrectly. What I meant is that the water for espresso bypasses the remineralization filter and the chiller. It's still RO water.

Given that, do you see any reason to prefer one or the other when testing for bacteria?

Why not test them both to start out with?

I bought the single-test pack. Maybe this was a shortsighted purchase...