This is probably the hardest jump in the game to master, and its god damn annoying to do. The idea is to shoot out of the water and propel yourself upwards. Well, here is how to do it (whether it works for you is another thing). The first way to do it is to go under the water and touch the side of the pool that you want to jump out from. Then face upwards and go forward to launch yourself out of the water, and as you are being ejected from the water, press jump (or tap it to make it easier) to boost yourself off the ledge of the pool. This is the general method and should work most of the time. The other method is to stay on the surface of the water and hold strafe against the side of the pool you want to jump out from. Then, whilst you are holding strafe (so you are pushing against the wall and facing along the line of the pool) slowly move the mouse inwards towards the pool, which generally propels you up and out of the water.There are other methods to water jumping, but finding the best method is best left up to yourself after trying to the above two methods. Good luck!
Speed Jumpsexample: speedjump from cells to the upper rocketlauncher and all the way to the rockets by water / speedjump from yellow armor to the ammopack crate to the light by armor (I think you mean mega here)
#2: To jump even higher, this is the way to go. Instead of staying on the surface, go straight to the bottom. Then, look straight down, then press fire and move backwards at the same time, or hit fire a little bit later to be sure you wont get stuck. Be sure to still look down while pressing backwards. And DO NOT PRESS JUMP!
Or you can do as I do, angle the runup so you run in a line exactly 90 degree on the healthpacks/wall in front of you. Then as you move next to the 3rd step while still standing on the 2nd step, quickly strafe right, turn right and press jump twice in order to doublejump off the 4th step.