It rained quite heavily for the whole week in Sydney last week, and in the weekend we went to a friend's house for lunch. Their neighbour at the back, who's land is at a higher level was building a 2 storey house.
Other than the non-stop annoying noise and dust, our friend mentioned about this leaking under their house during rainy days which only started after the builder installed an underground water tank between the 2 houses. And the photo below is what it looks like, you can clearly see water running from certain area while other parts were completely dry.
Suggest them to take some photos/videos and report to the council asap - specially before the construction work finished and the council issued the OC. Obviously it has to be somehow fixed and would be quite concerned if the water could cause any damage to my friend's house. Things like this would surely brought some delay or extra cost to any construction work.