Hummm. Maybe but ask to check the readings just in case: salinity, PH, KH, Nitra, Nitri and Ammonia. Better to be safe then sorry.
Also, if it's water from their tanks, check that all their fish are OK and healthy.
Like the post above says, test it. Also ask the folks at the aquarium if the water is good for use in a home aquarium. If everything checks out ok I would say congrats on finding a free water source.
You know wes I have heard of that place by a couple of other people who use the water. Never tryed it myself, the people I have talked to say it is good quality water, let me know if you stat useing it and how it works out I might try it myself. Good Luck