Varied TDS Readings
 

I've got a Aqua Safe RO unit that I put some new filters and RO membrane in a couple months ago. I've been testing it out but the TDS readings seem to be all over the place. One batch of water will be 2 and then the next batch will be 40. I don't understand the high readings since normal tap water is only 19 or 20 so how it runs through filters and comes out with a higher TDS reading I don't know. I've got it hooked up to a sink in the basement that is right beside the washer and dryer. Is it possible that other sources like having the washing machine on at the same time is contaminating the water? This might be a stupid question but can the TDS reading climb if the filtered water sits for a period of time? Thanks for your help.

yes actually mine comes out at 750-800 PPm from the tap :redface: when the RO/DI s going its at 0-1PPM then after the RO/DI has stopped it will climb up to 50-60

So would you say that's normal or could you be having the same problem?

My guess would be when having the washing machine on at the same time you don't have enough water pressure for the membrane to work efficiently.

The pressure guage still shows 50 to 60 on average.

I believe the membrane is most effcient at 80 psi.

K, so I've tested it over the last 24 hours and the reading is substantially less when its first filtered (2 to 6) than after its sat for 24 hours (30 to 50).

Thats the TDS of your saved water after 24 hours? If that is you have something leaching into the water from water pail you are saving the water in I would guess.

+1

But additionally, you should absolutely be getting 0 TDS coming straight out of the RODI unit. Run the output from the RODI into a clean glass and check the TDS. It sounds like you're getting contamination from your storage vessel.

I just tested it right out of the RO unit and it's reading 6. Could I have installed the RO membrane incorrectly? It didn't look like there's much to screw up in the installation.

I always let my RO/DI run for 5-10 minutes before I start saving any of the water. The water in the canisters is sitting there with everything they have filtered out so it is best to let it run for a bit first.

Do you have a DI unit hooked up as well? You should be getting around 98% reduction in TDS from the RO membrane alone. Given our tap water is around 22 ppm (that's what mine is right now) you should be getting a reading less than 2 or 3 if your RO unit is set up properly. And then the DI should definitely be getting things down to 0.

I had a problem with a home drinking unit that had a "post carbon" canister plumbed in after the RO membrane to add some TDS back in for palatability (taste) for human consumption. I was getting higher TDS readings than I expected. I ended up changing the order of the canisters to have two carbon filters plumbed consecutively before the RO membrane.

What unit are you using exactly? Unless you have a situation like the one I described above (with a "post carbon" canister) then something is amiss with your RO unit.

RO on it's own won't bring to zeo, that's why the di follows.

I just checked my water, 5 after the ro, then 1-2 after the di but then di last changed in July and haven't cal'd my meter so not getting worked up.

Have also noticed a rise in TDS after sitting and seen few other post the same.

So would you say that's normal or harmful?

not ideal since the idea of ro/di is to bring TDS to zero, not the end of the world as there's tanks out there using tap water.

I know I wouldn't be satisfied knowing I paid a couple hundred bucks for an RO/DI unit and I was still getting TDS.