From what I know is that all four are little pools of water that bubbles up…but I assume there are some subtle differences. What are they?
Jacuzzi is a brand name.
From here
I witnessed half of a humorous phone call during which all parties learned that the word “spa” is used differently in different areas.
Apartment Manager: “Hello, Boca Gardens.”
AM: “Yes we have vacancies.”
AM: “We have a lot of amenities, including a swimming pool.”
AM: “Yes, we have a spa.”
AM: “What’s in it? Uh. . . .chlorinated water, I guess.”
AM: “Oh! You mean an ‘exercise facility.’”
A friend used to work in the showroom of Kohler Company, which among other things makes whirlpool spas. He said it was dismaying how often people would come in asking about their “Jacuzzis”, which were actually their competitor’s product.
Ironically, when you order a “Spa” in the Netherlands you’ll get a bottle of mineral water. There’s a HUGE factory in the Belgian town Spa that bottles them. You can even choose between four types from Spa from four different wells. For those who are interested, Spa is a delightful little town only 50 miles from my hometown Maastricht. It still has a “past grandeur” kind of atmosphere from when it was visited by the early 1900 jet-set for its bath-houses and hot springs.
So, in the Netherlands Spa has become a generic name for mineral water, much like Jacuzzi has become a generic name for, well, spa’s.
“I want some spa”.
That sounds stupid.
I’ve never heard of #3. Any New England Dopers want to verify?