It depends on the type of water purifier you use. Gravity water purifiers and UF water purifier does not use electricity. If you use a RO water purifier, then it consumes about 20-25 watts of electricity for average daily use. Here is the calculation of the annual power consumption of a RO water purifier. Per day electricity consumption: 25 watts Per year electricity consumption= 25×360= 9125 Watts=9125/1000~ 9 Units. So a RO water purifier consumes about 9-10 units of electricity per year. If you use a RO+UV+UF, the electricity consumption will be more.