I know the Red Cross is heavy into the water purification effort - I can't recall the exact stats, but I think the initial commitment was clean water for 200,000 people (27 settlements). The US military and UN have even greater commitments.

Without a plan its status quo for Port au Prince, London at the turn of the 18th century - crapping in pails, dumped into the surface sewer gutter in the center of streets, running to gulleys and eventually the sea. With a sewer plan, you can lay lines to sewage treatment plants during reconstruction, train Haitians as engineers, and enter the 20th century if not the 21st. Primary sewage treatment is among the least expensive upgrades available to emerging nations - and with better than 50% of structures partially or totally demolished, running sewer lines to new construction is a no brainer. Assuming the Haitians have a plan. They'll need some engineers on loan for that, which shouldn't be too difficult from the US, Japan, EU etc etc.

Anyway, some part of Port au Prince will be rebuilt this way, and the part that is not will eventaully go the way that alot of older European construction did once central plumbing came on the scene - tear down (again) and rebuild (again). A house without plumbing can't compete with houses up the street that have it.