What should a 4 week old kitten be eating?

i have purina kitten chow should i mix it with just water till its soft and just let it eat that till its stopping and take away or is he old enough to leave the water/food in there at all times (so far ive not givin him any straigh up water just mixed in with food) i dont think he needs any milk anymore but not sure he was bottle fed cause his mother left him alone (by me) and am trying to get him on the right track thanks