Originally Posted by
h73kr
What system are you reffering to though? Potable water and toilet tank rinse supply having absolutely nothing in common, surely, or am I missing your point?! Toilet anti-siphon valve at toilet tank pervents unlikely event back siphonage of toilet charge water out of tank to stop chances of 'blue-ice' if toilet charge cap fails. Potable water system has nothing to do with toilet tank system.
If the lavitories are vaccum type with remote storage tanks, then yes the initial "squirt" of water before the waste is sucked away is potable water. As sys4 noted, it is an antisiphon valve in the system at the crapper that prevents cross contamination. Stick to beer and whisky if you feel you must rehydrate.