Shelf Life of Deionized Water

I use a laser welder for work on jewelry. It requires deionized water in the cooling system. Do you know the shelf life of an opened bottle of deionized water? Also, how long before the deionized water needs to be changed?
- David Roggi (age 58)
Bolton Ct. USA

I don't know the answer with great confidence, but can give some info. The main way ions will get in is via dissolved CO₂ from the atmosphere - the same process that is causing the oceans to acidify. This happens pretty quickly, but probably doesn't give enough conductivity to make problems in your cooling system. 

Here's what I recommend for both the shelf-life issue and the water-changing issue. The equipment manufacturer should have some specifications on the maximum conductivity (and maybe the minimum pH) for water in their system. You can get a conductivity meter and just check the water before adding and occasionally after use. Unless you need unusually low-conductivity water, the meter should cost under $200.

Mike W.

 

(published on 11/11/2013)