Any electrical appliance works with the consumption of electricity. Wattage mentioned at the geyser plays an important role in power consumption and also the time taken to heat the water.
More the wattage faster the water gets heated, but, electricity consumption will be higher. Normally instant geysers have higher wattage to deliver water faster. Storage geysers have nominal wattage which consumes less electricity.
In an electrical world, 1000-watt electrical appliances used for an hour will consume 1 unit of power consumption. Normally, electrical storage geysers will have 2000 watt power. This means, that using a geyser for half an hour will consume 1 unit of power consumption.
Always prefer to choose 5-star rated electricity consumption geysers. Which consumes very less electricity. Check the list of the best 5-star Geysers in India.