RO/DI unit tds meter question

Hello,
I am definately a firm beleiver in ro/di unit and only paid attention to the tds out which is 0 and today I looked at the in number which it read 001. Does it mean that my city water is not that bad. Could it be possible to read 000 on the in?

 

Not really.

 

You need three TDS readings to tell how good your tap water is and how well the RO membrane and DI resin are working.
First is the tap water TDS, second is the RO only TDS and last is the final or RO/DI TDS.

Any RO/DI should get you to 0 TDS regardless of the tap water condition, the big question is for how long will it maintain 0 TDS.

Do you have a dual inline TDS meter or a handheld TDS meter?
If you have a dual inline you should already have the RO only TDS and RO/DI TDS numbers. If you want to find out the tap water TDS a little trick is to sticak a temporary 1/4" feed line to the tap water or incoming side of the unit, temporarily install the OUT probe and tee in that line and run some water through the unit, this will give you tap water TDS.
If you have a handheld, draw a sample straight from the sink faucet for the tap water TDS, next disconnect the line between the RO membrane and the DI filter or install a tee and ball valve as a sample tap as I do for the RO only TDS and of course the final treated water is the RO/DI TDS.

With those 3 TDS numbers you can judge the condition of your tap water and RO/DI system. The RO only should be 96-98% lower than the incoming tap water in most cases and the RO/DI obviously should be 000. When you start to see anything other than 000 on a consistent basis its time to change the DI filter or resin as it is starting to leach weakly ionized contaminants back in to the treated water.

No, you will not find 0 TDS tap water, it would be extremely agressive and eat the pipes and fixtures it is delivered in which drives the TDS back up. Pure or 0 TDS water is agressive meaning it is always trying to get back to its natural "dirty" state, it will attract anything it can dissolve to get back to a stable condition.