For unlimited health, pause the game during gameplay and insert the following password: Square, Triangle, Left Trigger, Right Trigger, Up, Down, Left, Right.
Water Treatment Plant: Walk on air
Play the Water Treatment Plant mission. Go into the building. Go up the first ramp then go left. There will be a big window. Shoot it and when you get out there will be a bridge. Jump off the right side of the bridge. You will be walking on air.