According to the Water Research Foundation, the majority of residential hot water is used by four activities: showering, using sink faucets, washing clothes, and running the dishwasher. Figure 1 shows the hot water consumption by end use for a typical US home.

Figure 1. Cold water vs hot water breakdown by end use for a typical US home.

In practice, the amount of hot water showers, sinks, washing machines and dishwashers use depends on appliance efficiency, occupant behavior, and water temperature.

Showers

Showers are typically the largest consumer of hot water in the average home. According to the Water Research Foundation, approximately two-thirds (67%) of the water used during a shower is hot water.

The amount of hot water used depends primarily on:

• How often people shower
• How long each shower lasts
• The flow rate of the showerhead
• The selected water temperature

For example, an 8-minute shower with a 2-gallon-per-minute (gpm) showerhead uses approximately 16 gallons of water. If two-thirds of that water is hot, a single shower requires roughly 11 gallons of hot water.

Sink faucets

Sinks are another major source of residential hot water use. According to the Water Research Foundation, approximately 60% of sink water is hot water, although the exact percentage varies depending on the activity being performed.

The amount of hot water a sink uses depends on how long the faucet runs, its flow rate, and the selected water temperature. For example, a 2-gpm faucet uses four gallons of water during just two minutes of operation. If approximately 60% of that water is hot, about 2.5 gallons of hot water are used during those two minutes.

Washing machines

Clothes washers are another significant consumer of hot water. The amount of hot water a washing machine uses depends on the selected wash temperature, the machine's efficiency, and whether the cycle uses hot, warm, or cold water. According to the Water Research Foundation, approximately 20% of washing machine water is hot water.

Modern energy-efficient front-load washing machines typically use between 12 and 16 gallons of water per load, while modern energy-efficient top-load washing machines generally use 18 to 22 gallons per load. Older washing machines can use more than 30 to 40 gallons of water per load; at 20% hot water usage, this would be 6 to 8 gallons of hot water per load.

Dishwashers

Dishwashers also rely almost entirely on hot water to clean and sanitize dishes. The average US home uses more than 800 gallons of water per year for dishwashing, and nearly 100% of that water is hot water. Modern efficient dishwashers use between 1 and 4 gallons of water per load.