Just to add to this, you may be covered on your home insurance for this, especially if you have trace and access cover.Did they actually find the leak or just the pipe that was leaking?
Do you have a water meter to see how much water is leaking?
FWIW - if the water is coming up there, then it seems likely to be nearer to the house than the street.
On another note, I see you have older 'original' tiles under the units - they look like they could be possibly thermoplastic tiles from that picture. In which case, you (and the plumber) need to know that they can contain asbestos (as can the bitumen adhesive they are stuck down with) so don't go digging up or disturbing them unless you have them tested professionally first.