It's for hydro, and yea I've got a few large barrels that I can fill and have at the ready. I actually thought a R/O system would be what I needed, but I'd been reading that it won't deionize the water, which is really what I'm after. My water is super clean but it's coming out of a water softener and loaded with sodium ions. I could get the potassium pellets for the system, but those are 26 bucks a bag instead of the 6 for the sodium, and I need a bag every 2 weeks. So the cost of those would add up real fast compared to the up front cost of even just a deionization filter that puts out .5gpm. Those would last for 2500 gallons or so and cost like 20 bucks. Hmmm... choices.