Does D.I. resistivity drop with ambient air present in holding tank?

June 16, 2008

I work at an electronics company. Here at my work we have a new R.O. system with D.I. our out put is saying that we have at least one meg of res. but when I measure the resistence of the water it is at 750k ohm. Could that happen due to the presence of ambient air in the holding tank? Can some one please advise on how to also possibly fix this problem.

Thanks,

David Dadigan
electronics industry - Fort Walton Beach, FL, USA

First of two simultaneous responses -- June 17, 2008

Carbon dioxide in the air will dissolve in the water, creating ions in the water which will increase the conductivity (e.g., decrease the resistance).

If your water is used quickly, it shouldn't be a problem. However, if the tank is vented to air with some head space and the water is stored for a long period of time, you could see this.

If this is the case, try using a storage tank without a head space. If, for some reason, you cannot do this, you might want to look into some type of inert purge gas (such as nitrogen) to keep out the problematic gases. Realize, however, that some of this purge gas may dissolve in the water; that may be unwanted.

Christian Restifo
- Pittsburgh, PA

Second of two simultaneous responses -- June 18, 2008

Hello,

It is evident that te resistivity changes with the addition of other elements (substances). If your environment is not polluted, then your thank is contributing to this effect.

Jose Castellanos
- Minneapolis, MN, USA