What liquid do people use for their airlocks?

I have been using water for a while but have recently seen people who think this isn't best practice and is likely to get infected.

I have also found out that the sanitizer I use breaks down over time so likely wouldn't be suitable. I have taken to using dish soap for now but don't know if there is a problem with this practice.

I am currently avoiding vodka because of the alcohol duty in my country.