Water and waste water treatment plants are a key infrastructure element. Non-linear loads may affect their reliable operation. Non-linear loads in water treatment plants include variable frequency drives (VFDs), uninterrupted power supply (UPS), ozone generators, UV lights, computers and lighting. The process may be interrupted when harmonic current created by non-linear loads distorts the sinewave. The control circuitry of modern electrical equipment is designed for pure sinusoidal waveform. When operated under distorted waveform, repeated breakdown of sensitive electrical equipment will result in costly repairs. Critical loads in water and waste water treatment plants also require immunity against power outages and voltage sags.