GET EVEN

There are two choices that effect this.
You can do the Quick fix achievement, by solving the elcetrical puzzle in the first trip to building B, ignoring the inmate asking for freedom and then giving John is fix by turning on the light.
Alternatively, if you screw up the puzzle, you can just ignore John, and he'll stay alive.

The second decision comes in the second Building B visit. When you come to the Psycho puzzle. Only hit the left hand switch. Any others will cause John to die and give you a different puzzle to solve later.

When you get to the security station, he'll have the door locked solve the puzzle by finidng five valves to turn the water back on.

ALL VALVES MUST BE TURNED LEFT.
The first is to your right infront of John. Go in to the room he just opened. Turn left and in the corner is a sink, open the doors and turn the valve.
Go upstairs, directly on your right, as you reach the top, is a room. There is a valve on your right as you enter.
The last two is a pain in the bum.
Go out the room you're in, and go towards the bed that you need to scan for evidence. On your left is a room, once inside, on your left is the valves. Use your heat app to find out which two you need to turn.
It's the furthest right and then the furthest left, if you can't be bothered with that.
You'll know you got it right because John will scream his lungs out.

This achievement requires this achievement to be unlocked first:


If you did not save John, then you will need to replay this section of the game once you have completed it.

If you did, then this achievement will come naturally as you progress. Once you reach building C (after the memory John's final minutes), progress through until you see John on your left asking for you to sort out the water. You will need to twist several valves using the thermal app on your phone. Once you have done this, John will be happy and tell you the water has come back on. You will then unlock the achievement.