So probably over the last twelve months our water usage has been creeping up. As we live in Auckland we pay for water each month. We are a household of two, but I travel Monday to Friday so despite my love for long showers our usage should be pretty low. And often the bills are from estimates, so I assume it all evens out in the end. 

Anyway, we've had a slump in this corner of the cobbles, we removed a large tree that was disturbing the cobble when we bought the place. I'd assumed the slump was from the roots. 

Anyway long story short we heard water gushing from the corner of the house as it was very quiet this morning. It stops when the mains is turned off (the mains valve is about 2-3m from this point). 

I've attached some pictures, on the right is the broken garage/driveway drain (it's on my list, I want the whole driveway leveled and any remaining roots removed), the black plastic drain cover, I assume this over the actual water line itself. Will it extend all the way back to the mains valve? It honestly sounds like the leak is actually under the part I've uncovered. Is there any point me following the line back (down in the photo)?

Either way, is this a plumber call or Watercare?

I can hear the water hissing from where the red arrow is, but I don't know if that's just because the black pipe is cracked there. 

NB the blue bucket is on top of the large drain.