Q: How do VFDs save energy in a water treatment plant? A: As with a water distribution plant, water treatment plants have periods of high and low demand. During periods of low demand, VFDs can be used to slow down blowers to generate savings. Please refer to figure given below for additional details on a typical water treatment plant operation. As is evident below, water treatment plants have varying demands placed upon them throughout the day. In addition to this hourly variation of influent water in relation to the daily maximum flow rate for a given day, there is also variation of maximum flow rate experienced by water treatment plants.