I've grown in a small area and struggled with humidity issues before. First I found it best to put my humidifier near my air intake, I even got to a point I tried adding the humidity to my incoming air stream coming from outside my unit. I tried a variety of things to increase my humidity, like have you ever tried to dry towel out of the washing machine by hanging it to dry and closing your bathroom door and doing nothing else? It will spike the humidity levels, so I did it in my growing environment and everything worked out great as my RH jumped up. If my RH dropped during flowering to low, I would spray the walls with a spray bottle of water, and that really helped me a lot. I tried sitting containers of water out, and even hanging the towel down into a container of water, but it came with MASSIVE problems. I did try a water fountain inside my growing area and that really put off the most amount of controlled humidity in such a way I felt I could regulate it and know what to expect from day to day. The towel worked great in the winter time when I need lots of humidity, and then different towel materials and the sizes of them also depended upon how much humidity they put in the air and I have no control over it. I even put a fan behind the fountain so the air blew over the fountain to raise the humidity levels even more.
As for does it matter about the mineral content of the water? I deal with some really hard water, so minerals are a real problem for me creating nonstop problems on my humidifier so I learned right away it's cheaper to use distilled water over replacing units and parts. Then I was reading a comment one day on a carbon filter, the company was saying "they will not warranty the carbon filter because the person used something beyond distilled water for their humidifier which was the cause behind the carbon filter failing". I've never heard anyone say something about it before, but I have lived near the ocean and know how salty the air is, so I'm not going to debate if the minerals really do or don't end up in the air and could actually clog a carbon filter, it seems like it could be a legit thing, even though I've never heard of it before.
One of the ways I got around the temps spiking when I don't exhaust the air non-stop.. I used a mixed flow fan to pull air from the bottom of the wall on a straight metal duct about 12-inches off the floor so I don't pick up as much dust and dirt, and then I brought it up to the top of the wall with a 90-degree elbow and blasted it across the top of the lighting and plants, since CO2 is heavier than air, I thought it was going to have a double duty. All I know is I got my air temps to stabilize from the ceiling to the floor, my exhaust fan is on an "Sentinel DEC-4 environmental controller" I picked up on eBay for like $70. My plants are thriving for it and it was what really helped me get everything under control and balanced out for the best growth and results. But now I was looking at those AI controllers which do it all for you they have been coming out with and getting excited about how easy it's going to be to control your environment now. Somethings I did notice about the whole air pipe with the fan mounted on the wall to move the cooler air up to the top to cool down everything. My root temps got warmer, the humidity really stabilized more after a week, and the changes were different when I was running hydro, versus soil or coca because the air coming over the top and having warmer temps at the bottom changed watering schedules because it put more humidity into the air. Which led me to having to reduce the food as they evaporated more water. I also noticed that my fan that blows through the canopy was also more effective at managing the micro environment around the plants and they got denser with less issues. I assume this is because I had more air being exchanged from the ceiling to the floor.
