Leak detection
I don’t know if this qualifies as a Commercial Real Estate question but here goes.... I have a water leak at my shopping center. 0.002 MCF every hour , that’s roughly 15 gallons an hour. I couldn’t find where its leaking. My plumber went thru all the fixtures and couldn’t find anything. He suggested Sonar leak detection. It sounds expensive . 
I contacted a sonar company ,  but while I wait to hear from them, i thought I would come here and pick the brains of the greatest minds on reddit.
What does sonar testing entail? Is it expensive and is it guaranteed to find the leak.

Edit: I’m sorry I wasn’t clear, it’s not a roof leak, the water company says there’s a leak somewhere that’s affecting my water bill. 15 gallons an hour. The sonar test is to find a leaking pipe or fixture or something .
[{"id": "fov742h", "text": "as a property manager I have never used or heard of this type of test.  Usually a flood test is what i have done.  That is literally where they take a hose on the roof and flood different areas to see when it starts leaking.  Water travels, and can travel far.  \n\nOne thing I will say the only way to fix a leak that keeps coming back is to reroof the area.  It just seems to all be a gimmick at the end of the day though, get you to buy you a roof and to fuck you on the warranty somehow.", "replies": [{"id": "fov7tg6", "text": "As I said in my edit, it\u2019s not a roof leak ,  these new age  water meters can pick up leaks.", "replies": [{"id": "fovayez", "text": "then you shoud camera the line and they can tell if the pipe has been disengrated or there is a hole.", "replies": [{"id": "fovc01n", "text": "I suppose that would be my next step after isolating every unit one at a time", "replies": [], "depth": 4}], "depth": 3}], "depth": 2}], "depth": 1}, {"id": "fov7w6f", "text": "I have been through this kind of thing quite a few times. The first thing to consider is where the meter is located. Typically, everything on \u201cyour side\u201d of the meter is your responsibility, and on the other side of the meter is \u201ctheir\u201d (the water department) responsibility. If you\u2019re getting a confirmed usage/leak, then the assumption is that you know it\u2019s on your side of the meter. If the meter is at the street, there\u2019s potential that you could have a leak between the meter and the building. That can be an expensive fix. If the meter is in the building, you could still have a leak from the tap to your meter, but it wouldn\u2019t be accounted for. \n\nCan you isolate the units for usage? Say you have one meter and five units, are you able to shut off the units starting at the end and work your way backwards to see if there\u2019s a problem in line? You could have a leak in the ground, and that fix is substantial. \n\nYour plumber may take offense to your suggestions, but I promise it\u2019s worth fleshing out. I paid an HVAC crew a whole day of work to troubleshoot a package unit that wasn\u2019t heating and the crew leader finally determined that everything was completely fine, only to learn that the gas had been shut off because the tenant hadn\u2019t paid it. That created a standard procedure to check gas shut offs first for every \u201cno heat\u201d call. \n\nIf you need anything, feel free to reach out.", "replies": [{"id": "fovb0tx", "text": "So your saying shut off all the units at the sub meters overnight and see if I still get .002 usage every hour overnight? That would indicate a leak between the meter and my building. Mind you the meter is across my parking lot in a vault in the sidewalk. If there\u2019s a leak it would be in under my parking lot.\nThat should be my first step, if it\u2019s not there then I could shut 4 out of the 5 sub meters every night for 5 nights to single out the one with the leak. That\u2019s brilliant.", "replies": [{"id": "fovgfo2", "text": "Do you see any vegetation that seems unusually higher growth?   Any wet spots in the parking lot?  Any cracks seeping water?   What kind of soil is there?  Florida sand that would absorb 15gph?  \n\nThat\u2019s a lot of water to not show up somewhere.", "replies": [{"id": "fovheh2", "text": "It\u2019s in Cleveland , I haven\u2019t noticed anything out of the ordinary in the parking lot or in the units. The city just put a high tech meter in the vault, that\u2019s when they started reporting a leak and offering an hourly reading.", "replies": [{"id": "fovj19q", "text": "Also, because you\u2019re in Cleveland, your water line is likely 48\u201d or deeper in the ground. If it\u2019s a big property, the tap may be substantial (bigger than 1\u201d). The line should still be continuous, depending on year of construction. The only time water line would be segmented (pipe instead of extruded line) would be if it was say 25-30 years old or older. Also, it would have to be fairly substantial line (3\u201d or bigger).  You\u2019d see that in subdivisions where there\u2019s dozens or hundreds of homes, not as common in commercial.", "replies": [{"id": "fovjk5l", "text": "The building is well over 40 years old.  Maybe it\u2019s just falling apart .", "replies": [{"id": "foww9u5", "text": "If the building is that old, the likelihood is that the water supply line is iron pipe. It does break down over time. So, don\u2019t be overly surprised if that\u2019s the weak spot. Also, if the valves you have to each unit are gate valves and not ball valves, they may not seal all the way. This would cause you to get faulty readings.", "replies": [], "depth": 7}], "depth": 6}], "depth": 5}, {"id": "fovjhm7", "text": "Process of elimination then. Turn off all the units and check the main line.", "replies": [], "depth": 5}], "depth": 4}], "depth": 3}, {"id": "fovi5gr", "text": "That\u2019s the idea. I\u2019m in Toledo, if you need any help. Been down that path a bunch.", "replies": [{"id": "fovit7z", "text": "Thanks I appreciate it", "replies": [{"id": "fovj4vb", "text": "You a poker player or a gun guy? Or both? \ud83d\ude02", "replies": [{"id": "fovjp4s", "text": "Both of course! \ud83e\udd23", "replies": [], "depth": 6}], "depth": 5}], "depth": 4}], "depth": 3}], "depth": 2}, {"id": "frdu270", "text": "Hey just to update you, here\u2019s what happened. I followed yours and everybody else\u2019s suggestions. I shut off the water to every unit one  night at a time until I narrowed it to one tenant (the nail salon).\nThen I had to basically do the same thing inside her unit where I isolated all the different pipes being fed from her sub meter one night at a time.\n\nI ended up isolating 2 pipes ( hot and cold ) that went to her bathroom. It traveled roughly 20 feet underground to her bathroom &amp; Since I wasn\u2019t about to break no concrete for that, I just cut the pipe, and rerouted the lines thru her wall and ceilings with Pex pipe and shark bites. Problem solved!\n\nIt was a tedious process of turning the water on and off  and monitoring daily and getting these tenants on board. The repair itself took a few hours. The planning and executing took almost a month .\n\nI\u2019m just glad it\u2019s over and that I gained the experience to immediately find the problem a lot sooner.\n\nThanks!", "replies": [{"id": "fre7xxk", "text": "It feels good to have a job like that done, right? I\u2019m glad it went well for you!\n\nJust a thought of past experiences... make sure that the space in the ceiling will stay above freezing temps year round. I had a crew do work for me that decided my process was \u201cdumb\u201d and they had a better and easier path. So, they ran everything in an attic. Above the insulation. In northern Ohio. The first cold snap told a great story. Thankfully nothing ruptured, but we had a lot of work to do to get it right. \n\nMy dad always said, \u201csome people are so dumb, they couldn\u2019t pour piss out of a boot unless the directions were on the bottom.\u201d I\u2019ve found a lot of those people in just about every business I\u2019ve been in. Scary, really. But, now I know why Velcro shoes are still sold.", "replies": [{"id": "fre8fu8", "text": "I didn\u2019t even think of that. It\u2019s barely above the drop ceiling line,I\u2019d say 11 feet up. I think it should be fine. \nYour right about stupid people, true what they say; common sense is the most limited of all natural resources.", "replies": [], "depth": 4}], "depth": 3}], "depth": 2}], "depth": 1}, {"id": "fovji3m", "text": "Yeah I did that.  Think it was charged hourly and was maybe 200 an hour or so?  I did it on a 30ksf or so mixed use retail/residential building.\n\nYou will have to eliminate all water use while testing.  They basically shut everything down and listen to the pipes for water movement as they reopen to determine what sections of the property water is moving too and from.  \n\nIt is a worthwhile service after you give up but id try isolating the units like you sound like you are going to do first.  Its essentially a fancier version of that where they can tell instantly if water is moving or not.", "replies": [{"id": "fovjwym", "text": "It\u2019s just a coordinating nightmare with the tenants being out due to Covid-19. Getting them all together to schedule a water shut down. I\u2019ll figure it out either way", "replies": [{"id": "fovky2k", "text": "Good luck.  When I did it getting everyone to just not use water was by far the most frustrating part.", "replies": [], "depth": 3}], "depth": 2}], "depth": 1}, {"id": "fovnxvd", "text": "Instead of dealing with tenants, go to the site late at night and check the numbers on the meter wheels.  Check an hour later and verify that the meter is in fact turning, indicating the water usage.  \n\nA client of mine showed a 200 gallon spike on Tuesday mornings after smart meter install and it took a few emails and a double check of the meter to solve.", "replies": [{"id": "fovpz1l", "text": "I wish it were that easy , the submeters are deep in their units . Like in their back rooms", "replies": [{"id": "fovsmul", "text": "I meant check out the main meter to see if it is showing usage before even dealing with tenants.", "replies": [{"id": "fowv16y", "text": "I think the whole point is that it is showing usage, when it shouldn't be, that's how they know there's a leak.\n\nOr are you saying the transmitted signal may not be correct and to physically check the analog indicator to confirm if there even is a leak at all?", "replies": [{"id": "fowy925", "text": "Yes, exactly.  The 'leak' shows up as soon as the digital reader is insalled...worth a few min to see if the physical meter is spinning.", "replies": [], "depth": 5}], "depth": 4}], "depth": 3}], "depth": 2}], "depth": 1}, {"id": "fovp5xw", "text": "cut off your water supply as far up stream as possible.\n\n&amp;#x200B;\n\nthat should help identify where the leak is\n\n&amp;#x200B;\n\nalso may be a busted meter.", "replies": [], "depth": 1}, {"id": "fovq095", "text": "If you have accessible submeters on each space you should take a look at them early in the morning before the tenants open to see which meter is \"spinning\"\n\nNot sure if it's any cheaper than sonar testing but you could also camera the line to try and find a break.\n\nI've also found that sometimes the water dept themselves are incredibly helpful in issues like this - YMMV but I've had a water dept in a large city spend hours tracing meters to help me find a leak - for free.", "replies": [{"id": "fovql3p", "text": "The City of Cleveland water department is absolute shit.  They won\u2019t help with anything on my side of the meter", "replies": [], "depth": 2}], "depth": 1}, {"id": "fovsxbh", "text": "Well what happens is on the water company website you can pull hourly reports. And that\u2019s where the website notified me of a leak. The actual meter is in a vault on the sidewalk . Hard to get to.", "replies": [], "depth": 1}]