If the Council have not taken over the estate then the responsibility for the water network within the common areas is the builders.
If or when they take it over, they will assume responsibility for the water network. They will only take it over when the builder requests them to do so and only if all the services have been certified.
Any pipework within your site is your responsibility. You should be glad the builder fixed the leak outside your door. He should however fix any damage caused to your front door.
As for the water accumulating in your stop cock connection box, it's common for them to fill up with water especially after heavy rain. Unless water is pouring out of it, I wouldn't worry.