Nelsen 75GPD Reverse Osmosis Water Filter
75 GPD is more than enough capacity to serve 3 humidifiers. The Nelsen RO systems have Twist Loc filters for easy removal and replacement without shutting the water flow off. You can swap these out in just a couple minutes. The parts bag includes fittings and hanger screws to get you started.
Filters are charged every 6 months for the Sediment and Carbon filters and every 24 months for the RO Membrane cartridge. Of course this depends on the input of your water quality.