^Welcome to Bluelight! :D
Yes, distilled/purified/de-ionized/spring water will work. Tap water will work too, but I'm not sure how the chlorine would affect your product (LSD cannot be stored in tap water for this reason), and the "hardness" of the water may determine the solubility level you can achieve. If using de-ionized, spring, or tap water you should boil it first to sterilize it.
You are much better off using vodka though. The reason for this is that the water is distilled and purified, and it contains 40% ethanol which will naturally prevent bacterial and fungal growth. You cannot guarantee a pure solution for long with just water unless you bottle the solution in a vacuum at high temperatures, and even then there's no certainty the product wasn't contaminated. Quite simply, as soon as you unseal your distilled water to make the solution, it is already contaminated and it is just a matter of time before it spoils to the point of inedibility. Storing these compounds in water is just a short-term solution if you know you are going to be using it up fairly quickly.
Stored in vodka, the solution should last you very long time.