Which Cruise line are you at?
Does that make a difference? NCL ftw!
Not at all. It's 2500-3500 ppm. You can't smell or taste the salt at all.
Salinity is typically measured via specific gravity. Typically that runs 1.02450 g/ml for full strength sea water.
h202 = hydrogen peroxide. In concentrations over 35%, the stuff can be explosively volatile.
It's not toxic but a strong oxidizer. Hit up the MSDS to see just how dangerous it can be.
UV irradiation is expensive to operate and maintain and requires constant monitoring for effectiveness. It's generally inert like ozone but if the dwell is high enough and levels sufficient bromines can be produced in the presence of salt water. Typically we're talking multi kW sterilizers with too little flow.
Straight sea water has an advantage too - it can be skimmed! The problem with this could come from people using sunscreen and other skin treatments containing excessive oils, etc.