# Can I tell where a leak is in a vertical water pipe based on the water pressure at the bottom?

I have a buried water line with a leak in it and I want to locate approximately where it is. The line runs uphill to a storage tank. I've isolated the leak to one section of the pipe. The diameter of the pipe is 1.5" and the isolated section is about 300 feet long. If I measure the water pressure at the bottom of the pipe it is at 42 psi. This is after letting the pipe sit overnight with no water pressure coming into it from above so I assume that all the water in the pipe above the leak has drained out. Is it possible to tell roughly how many feet in elevation the leak is above the bottom?

• @Skywalker answer is right. You can only get the height of the water. You can only get the height of the leak if you let the water drain down to it. So if you measure the pressure at the bottom, you need to wait until it stops falling. Actually, that will be an asymptote. It will slow down before it gets there. Actually, you might speed it up by letting some water out the bottom. – Mike Dunlavey Feb 13 '15 at 13:35

IF all of the water above the leak point has indeed completely drained away, and the water is completely stationary throughout the pipe's entire length (those are important "if"s), then your problem is quite straightforward!

With the density of water, we can easily come up with a direct relation between water height (regardless of the horizontal path taken to get there) and the corresponding pressure at the bottom.

Check out this table for a quick reference: http://www.engineeringtoolbox.com/hydrostatic-pressure-water-d_1632.html

Looks like the leak should be just under 98 feet up (vertically). Of course, you'll still have to work out how that number maps to a position on the hill!

• One point to check: is the reported pressure gauge pressure or absolute pressure. If the latter (unlikely), subtract 14.7 from the reading and then proceed as @Skywalker indicates – DJohnM Feb 12 '15 at 20:46
• Agreed! That would instead indicate an elevation just over 60 feet. – RobotZombieLord Feb 12 '15 at 21:17
• I checked the pressure again this morning and it is holding steady at 42 psi. And the reported pressure is gauge pressure. So I will next figure out how to measure up 60 feet vertical and start digging! I'll let you know the result. Thanks for the help – Vic Cooper Feb 13 '15 at 17:20
• @Vic, it sounds like you may have misinterpreted that last bit. Since your measurement represents the gauge pressure, that means that your target is 98 feet- not 60! – RobotZombieLord Feb 13 '15 at 23:27
• Thanks for the clarification. It ends up that I was able to find the leak with just 10 minutes of digging! I had a hunch that the most likely place to find the leak would be where we transitioned from one type of pipe to another. Knowing that it was high up in the line (60 to 90 feet) was an essential clue. Thank you all for your help. Much appreciated! – Vic Cooper Feb 16 '15 at 17:56