From the Miriam-Webster Online Dictionary.
Definition of RIP OFF
1 a : rob; also : cheat, defraud
b : steal
2 : to copy or imitate blatantly or unscrupulously
3 : to perform, achieve, or score quickly or easily <ripped off 10 straight points>
From the Macmillian Online Dictionary
1. to cheat someone, especially by charging them too much money for something
"Tourists are worried they'll get ripped off."
"This government is ripping off the country."
2 to steal something
"Cars get ripped off all the time around here."
I'm not aware of the pricing of the bottles of water in the States so please forgive me, however here in Australia, a 750ml bottle of Pump branded water (approx 25 ounces?) retails anywhere from approx $2.70 at the local supermarket to $4.50 at the garage around the corner. One deli charges over $5.00.
Now if any of the above were trying to charge me $10 for a bottle that size, then yes, I'd feel ripped off. But businesses are in that very industry to make money. Profit margins are getting tighter and tighter across the markets and consumers expect bigger and deeper discounts more and more often. So of course they have to have something they are going to actually make money on, simply to compensate for the items they sell at cost or just over. And it doesn't matter whether they run a hotel or a corner shop.
The last hotel I stayed at in Sydney had a 1.5L bottle of Franklins water for $8. I went downstairs to the 7-11 to buy my snacks and drinks. Not because I perceive it as a rip off, but because everyone is in the business of making money, and it's up to me to decide who I allow to make money from me.
During the working day when I'm out, if I'm not near a supermarket, I will quite happily pay $4.50 for water if I need it.
The size of the text on the label isn't underhanded at all. I've always worked on the rule of thumb that nothing in life is free so where's the price tag? Your drinks in the spa were guaranteed to have already been built into the price of the treatment package. As would have been snacks and your "free" gift.