Presumably, yes. Although there are formulae to convert water use to an amount of energy consumption (which takes into account processing, pumps, etc), they are

Presumably, yes. Although there are formulae to convert water use to an amount of energy consumption (which takes into account processing, pumps, etc), they are probably referring to the energy to heat water. 1 watt for 1 year is (1W * 24h * (365d/year)) * (1Wh/1000kWh) = 8.76 kWh, or ( * 3412 BTU/kWh) about 30k BTU. The average bath is about 50 gallons, or ( * 8.35 lb/gallon) 417.5 lb. 30k BTU is enough energy to raise that much water by about 70°F (30k BTU / 417.5 lb). By that measurement, the Guardian takes baths 46.6°F hotter than their tap water. If that is too cool for you, you can take a smaller bath. It's worth noting that the conversions here assume you can transfer the kWh with perfect efficiency to heating water, while in actuality, all heating systems will be somewhat inefficient. It will actually take more energy to heat the water, regardless of the energy source used by the water heater. Edit: whoops, I originally misread and used 1.5 years and 1.5 baths. Calculations changed.