How to check for a water supply leak.

If you have ever had a water bill come in that suddenly increases significantly from previous months, with no known reason, your mind will eventually make it to the “Water Leak Panic” stage.  After all your habits have not changed, you know you don’t have a leak under a sink, none of the toilets intermittently fill up, the cost per gallon has not increased, and you just can’t think of any other reason why?

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Water leaks under a slab, in a crawlspace, or even out in a yard can cause significant other problems.  Well before you panic calm down a bit and take a moment to perform a simple diagnosis before calling that plumber.  Obviously the first thing to do is compare the actual meter readings on the current bill with the last bill to make sure there was not a billing error.  If that is not the case then take a moment to perform these simple steps.  You might just find it is a toilet leak, or other simple issue, that you can correct.  This first procedure is based on the expectation that you have a main water shut-off valve near the house.  If your main water shut-off valve is the valve on the water meter then go to the second procedure below.  Finally a brief description of checking for a leak in the sprinkler system is after these procedures.

Leak detection procedure with main water valve at or near the house.

  1. Make sure there is nothing in the house running, you have not used the hot water or toilet for five minutes (allows them to fill), there are no dripping faucets inside or out, and you do not see wet or damp interiors in bathroom or kitchen sink cabinets.
  2. Go out to your water meter and check the flow dial for movement.  Virtually all water meters (unless very old) have a flow indicator dial that looks like either a triangle , a circle divided into pie slices , or a sprocket.  These are the most common styles of flow indicator dials and example pictures have been provided below.  These flow indicator dials are very sensitive and can detect even a pin prick leak opening.  If you have a leak these dials will continually move (either slow or fast) in the same direction.  Be careful not to mistake a leak for normal water flow indications.  If they are moving slightly in one direction, and then the next, it might indicate flow back and forth through the meter as other users in the area draw water from the line your meter is hooked to.  Some meter covers (see picture below) might require a special key (see picture below) to open them.  You can purchase these keys at the local hardware store, Home Depot, Lowes, etc.  However some might have bolts requiring a socket wrench to open, and some towns use special locking covers.  To open and close the water meter’s valve you will also find it much easier with the water meter valve wrench displayed in the picture below.  These can be purchased at the same place you buy the water meter cover key.
  3. If your flow indicator is constantly moving then find your main water shutoff valve near or in the home.  Obviously this is not the valve located at the water meter itself.  Turn the main water off at the house main shutoff and go back to the water meter to see if the flow indicator has stopped moving.  If it has then the issue is after the main shutoff and somewhere in/under the house.  If the flow indicator is still moving then it is an issue between the water meter and the main shutoff valve that may require more troubleshooting, digging, etc., by a licensed plumber or could be a sprinkler system leak if you have a sprinkler system.  If the flow indicator did stop then turn the main shutoff back on and go back to the meter to see if the flow indicator dial is still moving.  If so go to the next step.  If not you might have had a strange anomaly and you should keep checking the meter regularly that day, and possible for the next few, to ensure the condition does not start again.  One word of warning about using that house main water shutoff valve.  Rarely do we ever touch these valves and problems can develop with them that either cause them to break or they might freeze up on you (rust or other debris).  If the valve does fail then you should immediately go back to the water meter and turn off the valve there.  If the valve is frozen then do not try to force it.  If you have a strange anomaly or main shutoff valve issue you should call a licensed Plumber to check and repair it.
  4. Go into the house and turn off all of the valves at each plumbing fixture, both hot and cold valves.  Be careful with these as well and do not force them if they are stiff and will not turn.  Don’t forget to check and turn off any exterior faucets.  Even drips on these exterior faucets can possibly cause the leak detector dial movement.  Go back out to the water meter and see if the flow indicator dial has stopped moving.  If it has then you do have an odd issue with one of the fixtures where it is leaking but you can not see or hear it.  If you have a hot water recirculating water system then it might also indicate a line leak under the slab and between fixtures.  You can turn on each fixtures valves one at a time while checking the water meter flow valve to see which one starts the flow indicator moving again.  That would at least help you isolate the problem fixture before you call the plumber.  If the flow indicator kept moving with all of the valves off then go to the next step.  Keep in mind that at this point you most likely did not have access to fixture valves for things like showers or tubs where the piping might be behind walls and no valves present or accessible.  The next step helps at least narrow the leak down to those fixtures.
  5. If after turning off your plumbing fixture valves (except ones for tubs and showers described before) and the flow indicator is still moving you now need to isolate the water heater.   For the water heater first turn off the electric or gas to it to help avoid damage if you forget to open the water heater cold water supply valve after this check.  Shut both the cold and hot water valves off if you also have a hot water valve (most don’t).  Read your water heater manual for the proper steps to shut it down completely without draining it.  Next check the water meter flow indicator again.  If the flow indicator has stopped moving then you have a potential problem with the water heater or the hot water output line.  If the flow meter has not stopped moving you have now closed off almost the entire system and gone as far as you can to isolate the problem.  There might be a leak in one of the plumbing fixtures that you have no individual control valves for like a shower or tub or there might be a leak under the slab.

Leak detection procedure when the water meter valve is the main shut-off valve.

  1. Perform steps 1 and 2 above.
  2. Turn the water meter valve off and watch the flow dial.  If the flow dial stops you definitely have a leak somewhere after the water meter.
  3. Perform steps 4 and 5 above.

Many times sprinkler systems fail and/or supply pipes become damaged and leak.  When checking for leaks you need to also check the sprinkler system.  This is an easy step and can even be performed before you check the rest of the home.  The sprinkler system should be equipped with a back-flow prevention valve set that is typically located in a valve box and near the water meter.   A picture of one is displayed below.  The valve set has two water control handles on it unless you have a very old sprinkler system.  If you do not see leaking at this valve set then either one of these valves can be closed to shut down any water flow to the sprinkler system.  If you can the better one is the valve closest to the water meter.  Check your leak dial and if the dial stops you have a leak in the system and need to have a licensed Irrigation Specialist check for and find the leak.  Just a word of caution that although a licensed Plumber might be able to perform this work the State of Texas does require the Plumber to also be a licensed Irrigation Specialist to perform work on a sprinkler system.

    If you are able to isolate the leak and stop it by shutting off valves to a plumbing fixture or appliance then you at least have some breathing room before you call a licensed Plumber.  You have also gained a better understanding of what the Plumber will do, show and tell you when they arrive for the leak testing.  Remember to always use a properly licensed Plumber for any work in your home.  Never use that handyman or unlicensed person for your plumbing work.  Doing so can potentially cost you a great deal more money later!

    Dallas Leak Detection

    Water meter with a sprocket shaped leak indicator

    Plano leak detection

    Water meter with pie shaped leak indicator

    Frisco leak detection

    Water meter with triangle leak indicator








    Richardson leak detection

    Water meter cover

    McKinney leak detection

    Water meter cover key

    Irving leak detection

    Water meter valve wrench







    Allen leak detection

    Back-flow prevention valve set for a sprinkler system.







    [tab: Links and References]

    Knowledge is power, but sharing knowledge brings peace!

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