Don't forget water purification tablets!

Even in areas where the ground-water still seems reliable so many refugees can be a problem. You really need experienced teams to look at where the well is, where the refugees go - and where the refugees "go" - to make sure there is no contamination now, in the next heavy rain, and in the next hurricane. It's easy for relief efforts to poison surviving groundwater, and it's happened before.

(the Bangladesh arsenic disaster is different, but is another example showing that above all else, existing clean water must be protected, and that being a well-meaning relief agency is no substitute for rigorous engineering assessment)