It is recommended to use purified or distilled water.
Purified water is water that has been filtered by any water filtration system, such as a counter top model like Brita, there are also units that are under the counter or whole house filtration systems but these get expensive.
Personally I don't recommend distilled water, see water debate forum for the reason why, but many if not most forums here on Curezone recommend drinking only distilled water, because they believe it has the ability to pull out of the body unwanted mineral deposits and other poisons. Also they believe that tap water is too polluted to consume and better to drink water that has everything removed from it.
The best I can tell you is test your water and make a decision from there. Water test kits can be purchased from Home Depot, Lowes or you can make a call to your local water treatment facility and ask them for directions on how to test your home water.
Personally I don't think it really matters...if you can add juice to the mixture and those minerals are not an issue then what's the difference? Isn't there minerals in the body? Isn't there minerals in green drinks?