As you know things such as bacteria and viruses like to grow in any kind of water especially hot water.
Sanitizers are used to effectively disinfect and keep water smelling fresh. The two most popular ones are chlorine and bromine. You can test these by using a test kit or test strips. Proper reading
for chlorine is 1.5 - 3.0 PPM and 3.0 - 5.0 PPM for bromine.