Over the past 12 years of motorhome ownership, we've stayed in Florida for up to 2 months, and snowbird in Mesa AZ 4 months, 5 times. Running coast to coast and north to south, we've come across all kinds of "local water", as supplied by RV parks and campground. Some tasted different, yes...but we've never gotten sick. Ever.
As far as "hard" water....where our HOUSE is....the water is hard. So....whattayado?
Never had an external filter, softener kit, for the house or the motorhome. The first time I winterized the motorhome I, per instructions, removed the in-line filter under the sink and replaced it with the supplied pipe with fittings. Never put the filter back. Never had a problem with the motorhome piping, pump or anything else. Never had a problem with the house (water and piping).
IMHO, put your money in the gas tank and enjoy your travels.