That would be a 3 bolt 'outlet', not inlet. Yes, water-cooling is a good tool to have in a turbo, but as stated before it is not necessary. There are BB turbos that are only oil-cooled as well. Turbonetics and Comp turbos are two examples. The just make their center cartriages out of a newer ceramic material. It better withstands heat than what most turbo BB center cartriages are made out of. They do not need to be water-cooled as well. I guess it is all what the turbo company prefers in turbo design.