Water quality is the single most important aspect of a good tank. Good water is a key factor in the long term success of a saltwater aquarium, especially one with delicate items such as corals. Over time, the use of "not so good" water will lead to the build up of bad stuff in your tank which may cause you to spend big bucks to remedy. Do yourself a favor and save yourself from headaches down the road.
Look into ways to make sure the water going into your tank is as clean as possible. If that means purchasing water or installing RO/DI, then do it. Trust me... i am an idiot when it comes to handyman work, but i was able to put in a RO/DI with no problems.