i would definitely use filtered or better yet R/O water, on a well system, often town water ahs chlorine, and this can be taken care of with a dechlorinater, but wll water has alot of other goodies in it, which may be unwanted in your tank, like iron, sulfur, or other minerals, often they are at levels that you won't visibly see, but are stilll present and it does not ake alot to give you problems in a tank
HTH