Hi
One word of correction: an absinthe fountain is used to pour water into the absinthe. There are lots of other devices for doing this - drippers, small spout pitchers and so on. The idea is to get a constant and very slow trickle of iced water into the green liquid. Why? This releases the herbal oils held in suspension in the alcohol and creates the louche. The potency of absinthe is in these herbal oils. The most notorious herb (plant actually) used in absinthe manufacture is grande worwmood (artemisia absinthium) and that contains thujone.
Alcohol is a GABA agonist. It stimulates the production of this neurotransmitter which causes drowsiness and sleep. Thujone is a GABA antagonist. It prohibits alcohol from performing that part of it's function. Absinthe is therefore a type of 'speedball', it's chemical constituents at once promote the production of GABA and opens its receptors, while also closing those receptors off. This explains the green fairy effect that absinthe has, as oppossed to just normal drunkenness.
Absinthe sold in US stores must test thujone free or <10ppm thujone. The norm in Europe is around 35mg/l or in some cases 100mg like
Century Absinthe You can easily buy them online but they do tend to rather expensive. The good news is you only need a little to experience the effect at a ratio of 1:4 with water and two glasses is quite enough...don't forget that this drink is very high proof alcohol
a louched absinthe is a right tasty treat, a lot like pernod/pastis. I wouldn't bother with the non-louching types (without anise), not pleasant.