Filtered drinking water fountains are located throughout the terminal in the following areas:

Terminal 1 M level after security between gate 4 & 6
Terminal 1 M level after security between gate 8 & 10
Terminal 1 M level after security at gate 21
Terminal 1 M level after security at gate 24

Terminal 2 Level 1 before security opposite Hungry Jacks
Terminal 2 Level 1 before security behind Cafe Vue
Terminal 2 Level 1 after security opposite Hungry Jacks
Terminal 2 Level 1 after security between gates 5 and 7
Terminal 2 Level 1 after security opposite gate 15B
Terminal 2 Level 1 after security opposite gate 16
Terminal 2 Level 1 after security between gates 16 and 18
Terminal 2 Ground floor after security opposite gate 4
Terminal 2 Ground floor after security opposite gate 5
Terminal 2 Ground floor after security opposite gate 16
Terminal 2 Ground floor after security between gate 16 and 18

Terminal 3 M level after security next to gate 5
Terminal 3 M level after security next to gate 7
Terminal 3 Ground floor after security next to the booking phones

Terminal 4 Ground floor of At Terminal T4 car park
Terminal 4 Ground floor before security beside baggage carousels
Terminal 4 Level 1 after security in the Tiger pier before stairs
Terminal 4 Ground floor after security between Jetstar gates
Terminal 4 Level 1 after security next to McDonalds
Terminal 4 Level 1 before security between Amcal and security screening

From the airport website