I have always dried out my carbon filters after I've finished filling my HLT with sparge water. This was more for logistics, as I brewed with propane outdoors, and needed to bring everything back inside, so it didn't make sense to me to keep the housing filled with water when I am moving it around.
Now that I am converting to electric, it will be possible, and I am considering, having a more permanent location for my water filter housings (I use two in series, both with carbon filters so that I can filter a bit faster and still get all the chloramine out). The thing is though, if I keep it in a more permanent location, I don't want to have to unscrew the housings after each batch, I'd rather just leave it as is.
If I do keep it filled with water, I would still purge some before filling the HLT for the strike water, but how concerned should I be about mold and bacterial growth?
Should I not even risk it, and keep on with what I've been doing with disassembling the housings and letting everything dry out in between batches?
What do all of you do?