Which Uses More Water: A Five-Minute Bath or a 10-Minute Shower?

Baths

• When comparing the water use between a five-minute bath and a 10-minute shower, it is important to understand that the duration of a bath does not matter. Unlike showers, which involve a steady water flow, it doesn't matter how long a bath lasts once the tub has been filled. What does matter is the size of the bathtub, which determines how much water is necessary to fill it. In addition, whether the tub is filled to the halfway point or completely filled determines how much water is used. According to the Alliance for Water Efficiency, filling a standard-sized bathtub to the halfway point uses roughly 20 gallons of water. However, to fill the tub up to the overflow valve uses 40 to 50 gallons.

Showers

• The University of Minnesota estimates that showering uses 5 gallons of water per minute. Therefore, a 10-minute shower consumes 50 gallons of water. Since the average tub uses 20 gallons at the halfway point and 40 to 50 gallons when the entire tub is filled, taking a long shower uses 30 gallons more than bathing in a half-full tub. Taking a long shower is either equal to or consumes 10 gallons more water than soaking in a completely filled bathtub.

Other Factors

• Using a low-flow shower head reduces the amount of water used per minute from 5 gallons to anywhere from 1.5 to 2.5 gallons, according to the University of Minnesota. Using the median range, showering would then be almost equivalent to bathing in half a tub of water, or save 35 to 40 gallons more than bathing in a full tub of water. Other factors include whether the shower is used at full-force; whether multiple shower heads and body sprays are in use and the size of these devices; and whether the shower is running continuously for 10 minutes, or if it is temporarily turned off while lathering, shampooing or shaving.

Testing the Theory

• Since these studies and evaluations are estimates that cannot account for individual factors, the California Energy Commission recommends you perform a simple test to determine whether you are consuming more water while showering or bathing. The next time you take a shower, plug the bathtub, and allow it to fill with water the entire time you are showering. Afterward, measure the fill line on the tub to determine if you have used more or less water than bathing.