Don't know if this is true for all water companies but last week I happened to look at my water meter. |It was going round like crazy and from looking at previous bills I was using at least 10x my usual volume. I called Wessex Water and a guy came out with a stick (high tec) and by probing the ground and listening marked the spot where he thought the leak was. As it was within my boundary I assumed that I was in for a big bill to sort it out. But no, they do a free leak repair service and credit you with any water lost above your normal usage. As I am on solid chalk there was no sign of a leak at the surface.
I have had two guys here all morning and have replaced about 5 metres of the black alkathene pipe (which goes brittle with age) with new blue piping using a mole and are reinstating the tarmac. Their leaflet actually says that within your boundary it's your responsibility but I am assured that it's a free service. Is this true of all water companies? 3 x FL1 2 manual + 1 auto
5 x FL2 4 manual + 1 auto
Now Discovery Sport P250 MHEV SE

I think it varies region to region and according to the nature of the repair.

My parents house had had a leak just outside the garage door leading to the back garden, well within their boundary. Seven Trent dug up and repaired the leak FOC. (this was a few years ago to be fair)

But then I read in the press about a guy a couple of weeks ago (cant remember where in the country) who had been complaining of a possible leak for years as he could hear running water under his garden. 5 (?) years of fault reports and no leak found even though there was 20k litres (IIRC) of leaking water a month. The water company eventually found the leak but refused to repair as it was under his garden within his boundary. Not sure what the outcome was.

I would say take your repair as covered by the water company

we had a rental that had incredible low pressure, on the terrace it was one of three properties that were still connected to the old mains supply, it took Yorks Water over a year to trace, they dug the rear yard and replaced the faulty tap 4 times, each showing no improvement, turned out to be a leaking pipe 18" before the tap

The pressure was so low the boiler would not pressurise after a fault was fixed

out of 30 properties on the new main, they could offer no explanation as to the reason why 3 properties weren't connected Former Mod/Member, with the most post & Chicken George Arch nemesis

Some water companies offer repairs like this for free from time to time. Sometimes they will replace lead pipes for free too even if they are not leaking. It's depends on how lucky you are.
Usually you are responsible for the water pipe where it enters the boundary of your property, so, if you've got a 50m front garden it's a lot.

I managed to get water mains pipe and sewage pipe insurance cover for £1 for 12mths! One of those auto renew policies, just remember to cancel it before it renews. It covers excavation, repairs and reinstating disturbed floors, drives or gardens.

As a plumber myself even a quid was too good to refuse.