i think in a traffic jam situation the water-air would beat an air-air. but imagine u park ur car for 4 hours in hot sun. the reservoir, radiator will need some time to cool down...most probably optimum by the time u reach home heheh..
water pump u can look for a bilge pump from pump shop. bilge pumps operate on 12V, used to transfer large amounts of water out of boats. its quite large, and little noisy too, but also quite cheap and powerful. some subarus and one toyota came wif a diaphragm pump for water-air intercooler. u can look at chop shop for those, good luck. agricultural diaphragm pumps are also suitable, try finding one that runs on 12V.
i've seen a drag kancil wif a water-air setup using iced water. at almost 2 bar boost it pulled 150hp. even at full boost you can feel the intake pipes cold to the point water condensing on the outsides of the pipes.and oh yeah it was using race fuel too.