Unrelated to the modding issue, but why would a storage organ somehow make them not need to drink?
Wouldn't storage simply allow them to drink several times at once and, you know, store it? They'd still require as much external water, though! Just timed differently.
In order to never drink at all, you'd have to have several organs different. For instance:
1) Water storage hydrator, AND
2) Superdwarvenly powerful kidneys, AND
3) A very long snout or similar so that when you exhale, water circulates inside and recondenses, like a kangaroo rat, AND
4) Some method of cooling themselves off other than sweating. Which can be tricky. Depends whether ambient temperature is generally higher or lower than body temperature (if lower, huge thin ears would help for instance, but that becomes counterproductive if it's hotter than body temp outside). And for example, you can make a snout as a new extended body part off the head, and then make it huge so it's more likely to take damage due to its size. etc.
If the storage gets damaged, then they have to drink more often, but not more water.
If the others get damaged, they have to drink more total.
(If possible)
Also, for flavor purposes, I'd mod the allowable hair colors for them to all be light colors =P