Quick RO/DI Question

[JeffG93]

Hey Folks -

 

So my RO/DI unit, which is going on 2.5 years now, is starting to show 1 TDS despite the DI resin being fairly new (and still over 1/2 blue, its the BRS color changing stuff.)

 

Any ideas what to replace to fix this?  Is it time for a new R/O membrane maybe?  The water going in is 5 TDS.

 

Thanks!

 

Jeff

[Origami]

Keep in mind that it could also be your TDS meter. To rule that out, try dipping the meter in a clean glass of distilled water. It should read 0 TDS.

 

If the meter is OK, try taking the water sample right out of the DI resin stage, before it's had a chance to flow through much of your tubing or landing in your reservoir. Finally, you should know that there's a high spike in TDS at the start of making water. If you're refilling your reservoir strictly on the basis of a level sensor / float valve, then you may be making very small amounts of water many, many times a day. The consequence to this is that your DI resin can exhaust very quickly. The solution is to make water much less frequently and in larger amounts. There are a variety of ways to do this.

[JeffG93]

Thanks Tom.

[Origami]

One way to deal with rapid DI resin depletion is to install an auto flush system that flushes the membrane just prior to water production starting. Another way that I've dealt with it is to install an electrically actuated solenoid valve (cost ~$25 or so) on the output side of the RO/DI system. Then you set a timer to open up a window of time several times a week (based on your reservoir size and consumption needs) so that you're producing water in larger batches. For example, if I went through 30 gallons of RO/DI a week (between water changes and top off) and used a 44-gallon Brute as a storage reservoir, I might set the timer up so that it only (opened up a window of time and) produced water 2 or 3 times a week until the the float valve shut production off. Since the TDS burst is only limited to the first minute or so of production, I get many more hours of the cleaner "4 ppm" water hitting the DI resin than the minute's worth of 75 or 100 ppm water burst at startup.