There are three computers. The first two are obvious. First, is in the first area in level 2. Second, is the commissioner's office (level 2). Third, is on level 4 in the little office off the side of air filtration. The third computer is tricky, you need to interact with it 3 times. First, before you do anything else in air filtration, second after you turn off the valve, third after you replace the filter but before you turn the valve back on.
-Per feedback from motter, please make sure you explore each option inside each of the computer interactions to get credit for this achievement.
-Per FullMoonBeaver, if you interact with the computer in Air Filtration before you do anything and just before you go to turn the valve back on (just twice), it will count for the achievement. Basically, you can skip the second of the three listed interaction on the third computer. Can anyone else confirm this?