The Electrical Energy per Order (EEO) is used to determine the removal efficiency of organic contaminants in a UV/ H2O2 system. EEO is defined as the number of kilowatt-hours (kWh) of electrical energy required to reduce the concentration of a pollutant by one order of magnitude (90%) in one cubic meter of contaminated water. The EEO has units of kWh/1,000 gal/order of removal. The EEO is dependent on water quality and is measured at the optimum H2O2 dose. It enables a direct comparison of the effectiveness of removing different organic compounds using UV radiation. Contaminants with greater EEO values are more difficult and costly to remove in comparison to those with lower EEOs. For example, the EEO values for MTBE and benzene are 10 and 2, respectively, indicating that MTBE is more difficult to treat than benzene. An EEO of 10 for MTBE means it would take 10 kWh of energy to reduce MTBE from 1,000 µg/L to 100 µg/L (90% reduction) in 1,000 gallons of water. It would take another 10 kWh to reduce the MTBE from 100 µg/L to 10 µg/L, and so on.