Re: Can you drink De- ionised water that they use to fill up car batteries?

Yes, But it is not advisable.   Deionized water is water that has 
undergone filtration and removal of specific minerals.  Depending on the 
system, deionized water although purer in mineral content may contain 
higher levels of microorganisms.  This is due to the fact that residual 
clorine which is added to many water systems is removed in the deionizing 
process.