That Bull Run water is the best. I'm surprised you feel the need for any kind of filter.
For what it's worth, I use our regular tap water without any special treatment for all the plants in the ground. They prefer rain water but even our hard tap water (sometimes with extra silty chunks) is just fine. My plants in containers mostly get the same water (I adjust the pH for them) but they all get properly flushed by rain water during our annual rainy season.
I wouldn't need a filter for my hose but it wouldn't do any good against the problems with our water. We have to change the filters between the street and the house all the time because they're constantly clogged. Whatever the gallon rating of a filter might be, that has to be cut 10-fold given our supply. And the other thing to bear in mind is that if your water is hard (salty), a carbon filter is going to do nothing to improve the situation. The only things that work are reverse osmosis (a relatively serious piece of kit), or what I do, which is to mix acid into the tap water before use. That does not reduce the salt but it does eliminate carbonate hardness, which is the basis for hard water having a high (alkaline) pH.
The one thing you absolutely do not want to use is softened water (which has extra sodium in it, and sodium is not good for most plants).
