I think it would be a cool Idea to add 5th category for nutrition called Hydration.
Depending on how clean the water source is, it should give an appropriate multiplier for nutrition.
Different sources could be
Salt water -> worst multiplier
Contaminated Water -> bit better
River Water/Lake ->
Purified Water ->
Purified Water could hook into the settlement system via a water purifier (similar to the waste filter), which could supply clean water to the town