Knowing a water pump's operational costs will help you purchase the most efficient unit and enables you to predict associated yearly expenses. Based on those predictions, you may wish to reduce use or invest in a more efficient unit. You also may need to determine the cost for a tax reduction or something similar. Calculating the total cost can be done by multiplying the power consumption by the cost per kilowatt hour.

Reference the unit's voltage and amps. This information should be listed on the pump's specifications.

Multiply the voltage times the amps to calculate the unit's power in watts. Divide this number by 1,000 to convert watts to kilowatts. As an example, a 115 volt, 2-amp pump produces 230 watts, or 0.230 kilowatts.

Multiply the pump's kilowatts by your cost per kilowatt hour. This figure is likely listed on your electric bill. For example, if you paid 12 cents per kilowatt hour, then you would multiply this cost by 0.230 kilowatts, which gives you an operational cost of about 3 cents per hour.

Multiply the hourly cost by the number of hours the pump is operational per day. For example, if you ran the pump 24 hours per day, you would multiply 24 times 3 cents, which tells you the pump costs you 72 cents per day.

Multiply the daily cost by 365 days to calculate the annual cost. For example, 72 cents times 365 gives you a $262.80 (£170.08) total annual cost.