Haiti has an issue with water because they have little drinkable water on the island & have to filter sea water. Which simply means boiling the water & collecting/cooling the steam which isn't as hard as it sounds. Can be macguyvered with two hot water heaters & a guarden hose.

First priority will always be treating the injured & finding survivors in that order. You can go 3 days without water & a week without food so a couple hours thirsty & hungery won't matter.

At best a militia will be an extremely local organization, one small town dealing with its own first.