Toilet Water

What would be worse is not having anything al all to eat or any water to drink. It's just the way you look at things that can make things seem to be wonderful. source

It sounds like some of the water in the bowl is being syphoned out. If there are more toilets on the same sewage pipe, then you will need to have an anti syphon pipe fitted to prevent this. This can also happen when your neighbours flush their toilet, and syphon water from your bowl when they do so. source

It is an inexpensive fix to replace the inner workings of the toilet. You can check if it is leaking by putting food coloring into the tank, wait a little while and look in the bowl. If the color seeps in then you have a leak, replace the flap. source

I am surprised it isn't mandatory all around Australia to have tank water for toilets. We don't get a choice as it is mandated a minimum tank size of 5000ltr with plumbing to toilets in our suburb. source

Round the bend, the waste pipe feeds into the 'stink pipe' which leads to the main sewer. The other end of the stink pipe is open to the atmosphere for dissipation purposes and to prevent any gas pressurisation of the sewer system. The water in the bowl is your seal between your bathroom and the sewer. As the stink pipe is open, any movement of air at the open end will cause the water to respond. source