I discovered a leak in my well house today. It is coming from the nut looking element (on the pic). My question is what the purpose of this nut looking element and how to fix its leak?

Any chance it could be simply tightened?

enter image description here

  • 2
    The fitting is a union. It may have been stressed or twisted and started to leak. It can be disassembled, cleaned and reassembled. Are there valves which allow you to isolate that section?
    – HABO
    Commented Feb 23 at 3:23
  • I am not sure. I will have to see. It is in the woods, 1.5 hours away from where I live. I am assuming it will need to be depressurized before disassembling? Why did not you reply as an answer vs comment?
    – i--
    Commented Feb 23 at 12:54
  • 1
    The comment contains a question, which means that more information was considered important before a good answer was provided. If there's been a spate lately it's in casual observations left as comments. :)
    – isherwood
    Commented Feb 23 at 13:42
  • The comment contains a question because I expand on the info in other comments(s) which was unknown prior to it. I am afraid if I'll be evolving the question with comments, it will eventually answer itself.
    – i--
    Commented Feb 23 at 13:50

1 Answer 1


That's a union fitting.

First figure out exactly where the leak is coming from. Water drips from low points like that nut, but it could be coming from the pipe threads or even a crack in the pipe at the fitting. Most likely the leak is between two flat surfaces pinching a gasket, where the nut supplies compression across the gasket.

To find the leak I tend to use paper towels. Dry everything and then tie a paper towel around potential leak sources uphill from the drip. If one of these gets wet, then you've traced the drip to an upstream location.

Assuming that the nut is the leak source, then try tightening it first (many would advocate for giving this a try before searching for the leak source, but for a steel fitting I would follow my own advice). Loosen the nut a quarter turn to break any corrosion-caused seizing and to get a feel for how much resistance is coming from corrosion. If there's still a lot of resistance even after working the nut back and forth a few times, then consider unthreading it all the way and cleaning the male threads with a wire brush. Go after the female ones too if you can get at them (the trick is to rotate the nut with one hand while the other hand presses the wire brush into the threads), but the male threads are low-hanging fruit.

To retighten the nut, don't get a cheater pipe for the wrench or anything. 8" of leverage and the full strength of an ordinary man is about the most torque you should apply. For leverage and to avoid unthreading fittings, use a second wrench on the hex faces behind the union's nut as you're torquing.

If that doesn't stop the leak, then there's probably a failed gasket between the two halves. Probably a flat one, because machining a groove for an o-ring is especially expensive in the case of steel. You'll have to get a new gasket (having the old one in-hand is helpful) and install it. Some silicone grease is nice to hold the o-ring in position long enough to fit things together again and tighten.

If the fitting is cracked, extremely pitted, or something else that requires replacement, then you'll need a pipe wrench to hold the pipes against rotation as you unthread the fitting's halves. For steel pipe you should use pipe dope instead of PTFE tape for sealing the union halves to the pipe threads. Be sure to first wire brush any corrosion away. I prefer not to use any oil for fear of its interaction with pipe dope. Pipe threads can be razor sharp, so I don't want to be cleaning them with rags and soap.

I could remind you to put the nut on before its half of the union, but you'll probably forget for your first union anyway.

  • Thanks for suck a detailed answer. "One" more question: I assume I need to depressurize the system first? If so, would turning the pump off and letting the water out of the tank do it?
    – i--
    Commented Feb 24 at 2:02
  • 1
    @i--, remove power from the pump before you take anything apart. Beyond that is a housekeeping problem. I would try to get the water drained from the pipe, so that would entail finding a drain downhill from the fitting. If that's the tank, then great. The tank should be downstream of any check valves, so if your fitting is downstream from the tank, then draining the tank will drain water from the fitting assuming that they're about level.
    – popham
    Commented Feb 24 at 3:49

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