Abstract: The humidifier for controlling humidity in a semi-conductor manufacturing environment provides a trickle water refill level control system for maintaining an accurate flow of refill water into the humidifier water tank. A water supply provides a substantially constant rate of flow of water to a conduit connected between the humidifier tank inlet port and the water overflow tank inlet port, to allow the excess water supplied to the humidifier water tank to flow to the overflow tank. The overflow tank has a float level control allowing for operation of the steam generating humidifier at higher steam pressures, and increased stability of the steam generation rate. A pressure equalization line is also connected between an upper portion of the humidifier water tank and an upper air reservoir of the water overflow tank for equalizing pressure between the humidifier water tank and the water overflow tank.