Can I top off with Distilled water?

Good to know about glacier! As long as your are always able to verify 0 TDS

 

When they change filters its the prefilter and carbon, both of which have very little to absolutely nothing to do with TDS, they remove suspended solid particles (TSS or total suspended solids) andchlorine not TDS or dissolved solids. TSS are in the 1 micron and larger size, TDS are in the 0.0001 micron size, much different.
Its the RO membrane that does 98% of the work and in our RO/DI systems the DI does the final 2% polishing. I have yet to see a Glacier or any other RO only machine produce 0 TDS water, its not possible since they are a 90-98% efficient device at best.

Vending machines do not have to meet any health standards in most locations of the country, they are only subject to weights and measures inspections to ensure you get a gallon of water for your quarter since it is sold by volume. Same goes for most bottled waters again since they are not regulated.

 

Hm... I'll skip Glacier here in San Francisco.

Unsafe Water Vending Machines- Can Be Worse than Tap Water! Health Risks of Drinking Contaminated Water

 

x2 up there on the glacier machines! Im with Saints fan, I've been using that water for awhile and my parameters are always in good shape. Its super cheap too.