Hello Win Yin, in South Australia (not sure about regs in other states) new builds are required to have a Rain Water Tank installed and plumbed to deliver this rainwater to the Toilet, water heater or cold water laundry outlets. This may be the pipework you are referring to.
You can test this by shutting off the tank water outlet outside and seeing what tap inlets are affected. You could also ask the builder of your home.
Kate
dreamer
Related Discussions
Bathroom design woes - what do we do with the pipes?
Q
should we paint the copper pipe?
Q
What to do about hideous pipes over front door!!!
Q
Unknown Buried Steel Pipe
Q
Compass Kitchens