I didn’t read the replies.
I had one of these installed in my mother’s house. Worth considering. She’s been extremely happy with it, and been able to manage any potential water problems from all around the world via their app:
Obviously I don’t know how your municipal water provider works, but ours will refund half the leaked ($$) amount if you provide proof of fixing it within a certain time. We had an underground leak on “our” side of the meter, and they refunded 50% of the excess, once I provided proof of the plumbers’ repairs. In our case, they examine historical usage for a particular period and predict what usage would have been without the leak.
Might want to check if yours has a similar program.
Thanks, I just called my water company and while they do have such a program for leaks, they said it doesn’t apply to running toilets. Bah.
I wasn’t aware there were such devices as the Flo Smart monitor. I’m somewhat tempted, although the price of the monitor plus installation would probably run around $800 or more, and since this is the only time in my life that such an incident has occurred, I’m not sure it’s worth it. Of course, if it was a real leak rather than a running toilet, it would totally be worth it, but I don’t live in an area that freezes, so I think an actual leak would be an exceedingly unlikely event.
When I’ve had the toilet running continuously, it’s been loud enough that I can hear the water running, so I was able to check and jiggle the handle to stop it.
Yeah, unfortunately the last thing my wife did before we left the house was to use the toilet and flush it, so hearing it running at that point was expected. And after we reached our destination 350 miles away, we couldn’t hear it anymore. 
For a while, up until about 6 months ago, the frequently-used downstairs toilet would sometimes leak from the tank into the toilet bowl after flushing. Then it started happening more and more often. After looking at the stuff inside the tank and doing a cursory Googling, it seemed that a major part of the works inside would need to be replaced.
So I let it leak for months, fearing the cost of a plumber. Silly me! All it took was a flapper replacement, which in the greater scheme of things is a cheap, quick, and easy DIY job. You just have to make sure to get the right size and type of flapper, and adjust the chain length so you get a complete flush.
I had a 10,000 gallon bill due to a leaky external water line resulting in a $600 bill plus, since the assumption is it winds up in the sewer, a $300 sewage bill. I phoned the city to ask if the latter, at least, could be forgiven since a literal swimming pool’s worth of water had not wound up going there. The one I spoke to said the whole bill could be forgiven once in a lifetime if I sent proof of the repair. I said how and when, the repair had already been done. When next month’s bill arrives he said.
Sounds odd but okay. I paid the utility bill less the water and sewer, the next month that portion was marked 30-days overdue. Call and get the same answer. The month after that I was on a long camping trip and had no internet connection or phone service. When I got back into town I found a message from the city had been recorded that morning. It was complaining the bill was now 90-days overdue and had to be paid that day or else it would be shut off.
I called and got ahold of a city worker who said she’d never heard of getting a water bill forgiven, there were no supervisors in that day and I had to pay the bill. No matter what I said I she kept circling back to that like a terrier at a rat hole.
I didn’t have any banking information handy on the road so I called my brother who paid the bill and I paid him back when I got back home. Since then, any time I call the city I ask for their employee number and explain they have brought it upon themselves.