R/O water smells skunky
 

I noticed on my last water change that my R/O water smells kind of skunky. Not over-powering, but definitely not neutral. It made me check my R/O unit and the TDS was 22ppm. I replaced the DI resin, pre-filter, and carbon 5 weeks ago. Does this mean that my R/O membrane is pooched?

Welllll ... possibly but not necessarily. 22ppm on the output is not great but at the same time it depends on how much it is going into the membrane. If it's say, 50ppm going in and 22ppm coming out, that's kinda lousy but if it's 450ppm going in and 22ppm coming out (in the south I get those kinda #'s but I'm not sure what it is on the north side, our water is out of different watersheds) then it's still doing its job.

FWIW, I replace my prefilters around the 6 to 8 week mark and I get maybe 3 to 4 weeks on the DI. I use colour changing resin but I also measure the TDS coming out and anything above 0 to 1 sustained (a small burst) means it's time to change the DI.

When I run my RO I have to flush the membrane for a good 5 minutes. The TDS surge from having it sit idle in between runs can get as high as 600 to 800. I close the flush valve as soon as it reads <10.

So I guess the question about whether 22 is bad or not kind of depends. Was that a sustained reading or was it part of a surge? If you read again in 5 minutes after running is it still 22?

If it is reading 22 all the time then I would say it is time for a new membrane. Typically, you should get up to about 18-24 months out of a membrane but it also depends on how high the TDS is going in and how often it cycles on and off. It's better to get a good long run less often than many smaller runs producing the same overall volume.

HTH

Anything higher than 5 and I replace the membrane. Burns the resin so fast at that point. My incoming seems to be around 200. I flush for a few minutes then run the unit but bypass the resin until the membrane outputs less than 5. Prefilters I replace maybe twice a year. I back flush before and after using the unit. A membrane lasts me about a year but I make very little water now it should last longer.

There have been a number of RO/DI filter questions lately and I'm still gobsmacked that people are throwing out all kinds of figures as to how long between changes of various filter elements but not ONE states how many GALLONS PER WEEK/MONTH they pump through the thing !!

The whole equation boils down to the quality of the water from your tap and how much of it you put through the system per unit of time.

Tony changes out his filters at 6-8 weeks ! I change mine once a year. Tony seems to get his water from a sewer line (800 ppm !!!!); mine's at 100 or less.

I currently have a system volume of about 35Gal and I change 5 gals each week. Tony has a much bigger setup and I don't know what his W/C regimen is.

All that to say, ignore any suggestions on when to change unless they tell you their input TDS, and how much they use it each week !

Personally, I think if the water SMELLS off then I'd dismantle the whole thing and clean it out -AND change out all the filters.

Hmm, all this talk about bypassing stages and flushing... I have a Vertex 100gpd RO/DI unit, it has an automated flush function that comes on for 15 seconds when you turn the unit on, and every 15 minutes of operation, but is it possible for me to manually flush it/bypass the resin?

I don't measure the TDS going in, but I do know that this pre-filter went from white to burnt orange about 3X faster than it normally does. I replaced the RO membrane about 6 months ago, which is why I thought I'd get more out of it, but it really seems to be burning through DI resin now. However, I do 45-50 gallon water changes every single week plus whatever is evaporating from my tank, so I think I probably go through more water than most people.

And in this case, it was a sustained 22pm. I did a water change, which practically drains my RO tank, and in the process I noticed the smell. I checked the unit, (which was already starting to re-fill my RO tank), and it was at 22ppm. I turned it off, and switched out the pre-filter and carbon cartridge (my next set of DI and R/O membranes haven't arrived yet), and turned it back on. For 5 minutes it skyrocketed up to 50ppm, and then very rapidly came back down to 22. By the time I went to bed, it was reading 17ppm, but today it's showing 33ppm.

What's the best way to run the unit? For example, my auto-top off pump is in my R/O storage bin, so as it tops off my tank, the R/O unit is always kicking on to replace the lost water, but it's only ever producing tiny amounts at a time. Is that bad? WOuld it be better to cut the water supply to the RO unit and let the storage tank empty a fair ways before re-filling it? I'm not sure if the way I'm running it is contributing to how quickly it's going through media, or if I'm just using more water than most and have crappy source water.

600-800 is the peak value of TDS surge. Nominal is 200-400. It seems to climb much higher than the input water while it sits there idle. That's why it's really important to flush the membrane otherwise you are replacing the membranes more often which is costly.

If you like spending money on replacing DI resin often, then go ahead & plumb your system to your ATO. I think it's been fairly well documented that short runs of an RO system with high input TDS is going to burn through DI media in a hurry since the RO membrane rarely gets a chance to stabilize at a low TDS output.

So yes, disconnect the system from the auto top off & only run it when there's an opportunity to produce at least 10 gallons or more in a single session. Another good idea is to produce at least 5 gallons of RO water only and only after you've done that, start sending the output through your DI stage. You'll need a T-fitting & a shut off valve to divert the RO water before the DI stage. Find something to do with the RO only production water, like making tea or coffee, or beer & bubbly drinking water. This way, the RO TDS has a chance to get to the lowest possible level before feeding the DI stage and your DI media will last longer.

If the prefilter is actually discoloured then it is way past due for a changeout.

The 100gpd membranes on the market have worse rejection rates than good 75gpd membranes. Unfortunately you will burn through DI much faster than proportionally than on a 75gpd.

That definitely sounds like a spent membrane man ... sorry. After about 5-10 minutes of operating mine I will get 0 out of the membrane. I'm using the DI basically to catch the residual TDS in the beginning.

Ohhhh. Unfortunately yes, you will kill membranes like kleenex that way. I had to learn this the hard way myself after going through 4 membranes in 2 years. One I can accept as bad luck .. two as really bad luck .. when you get to 3 or 4 though then there's a pattern.

Yes - only refill your reservoir once it gets empty and close to empty. That's exactly what happened to me. Ever since changing the way I do things (one long drawn out fill) I've gotten much much better longevity out of my membranes.

Wow! 600-800, that's huge TDS. I thought I read somewhere that anything over 500 is unfit for human consumption and water coming out of your tap is mandated by law to be below that or the supplier has to issue a don't drink or boil before use warning! My tap TDS is around the 210 mark & after flushing my RO system on start up I monitor the TDS for a few seconds after I close the flush valve & the restrictor kicks in. The highest reading I recall observing is in the low 100's, say about 118-120 depending on the time of year. I bypass this water into a waste bucket. It then takes from 3 to 5 minutes for the membrane to get TDS down to 1 or 2. Into a waste bucket it goes until I see a 1 on the TDS meter. After this I start filling an RO container for drinking water, making at least 3 or 4 gallons. Only then do I start sending the RO water through the DI stage. Colder water in winter actually helps the membrane produce a lower TDS sooner.

Thats odd. I expected that sort of spike at turn on (and in fact, when I disable the DI stage to make RO drinking water, I usually do it before I make tank water to flush the system) but I don't get that. It's 0ppm all the time and when it hits 1 I change prefilter, and carbon (and as it happens, for my current usage, usually the DI is about done as well).

Not sure why I don't get that spike.