The US Government estimates that:
Water heaters can have elements with a range of wattages. 3,500 to 5,500 are commonly available. There are two elements, but only one is on at a time.
Energy use in a shower includes the hot water dripping out of the tub spigot (around 1 gallon per minute) as well as water through the shower head. There have been great efforts to adopt low-flow shower heads. Equally important are leak-proof valves to divert water from the tub to the shower.
CO2 for the water itself is much less than CO2 for heating it. An estimate from UK Water is that collecting, treating and delivering water release 0.789 g CO2e/liter. An estimate from a small Italian town is 0.58 g/l. (Pounds CO2e per gallon are 0.0066 and 0.0049 respectively to provide the water, compared to at least 0.1000 to heat it.)
OSHA recommends 140F in the water heater to kill Legionella, and 122F at the faucets to minimize Legionella growth in the pipes while also minimizing scalding (Technical Manual Sec.III Ch.7 subsection V.C.3.a). A "tempering valve" at the tank can achieve both OSHA targets, and also allows 140F for washing machine water (discussed below).
The common advice to keep water heaters at 120F ignores the risk of Legionella.
Clothes Dryers are often listed as an example of heavy electricity use. Energy websites frequently say that dryers range from 1,800-5,000Watts, but list no examples. Manufacturers generally give higher numbers:
In laundries at health care facilities, CDC recommends 170F water for 25 minutes, or chemical disinfection (like bleach). They make no recommendations for residences.
Professor Gerba, ABC and CBS recommend (a) washing loads which are not bleached at 140F, (b) washing underwear last, using a cup of bleach in a cold water cycle to disinfect underwear and washing machine, and (c) washing hands after touching dirty or wet laundry (2005 update).
eHow adds recommendations for (d) washing linens separately, using 5-part laundry baskets to prevent cross-contamination, and (e) disinfecting the laundry basket with a spray.
Ikawa and Rossen report research that bacteria in kitchen sponges are killed by 12 minutes in a washing machine at 93F (34C) with ½ cup detergent and 1½ cups bleach followed by 60 minutes in a dryer (no temperature given). Alternatives are boiling for 5 minutes, or microwaving a damp sponge in a "storage bag" for 1 minute on high. Drying alone was not effective, even in a clothes dryer.
Professor LeBlanc does not report research, but recommends disposable dish cloths, or immediately washing cloths in hot water or bleach, not leaving them damp. She also recommends washing underwear separately from dish towels or dish cloths.
Park and Cliver ("Disinfection of kitchen sponges and dishcloths by microwave oven" Dairy, Food and Environmental Sanitation. 1997, 17(3): 146-149) provide more details on the microwave approach. They sterilized damp (wet then wrung out) cellulose sponges (7"x4"x1.5") in an 800-watt microwave. It takes 60 seconds to kill all bacteria in one damp sponge. Time would be proportionate for smaller sponges or stronger microwaves. A damp dishcloth (16"x14"x1/8") takes 3 minutes. Microwaving natural sponges damaged them. (doubts, other studies, more on kitchens)
Lysol has a manageable list of surfaces to disinfect. Wordpress cites bacteria counts for many surfaces, but gives few citations.
Tide recommends monthly bleach in high efficiency (HE) washers, which lack enough water to rinse all dirt and detergent out of the machine. Tide does not claim germ-killing ability, nor recommend water temperatures, except they say almost all stains (including underwear) should be washed in warm water after pre-treating 20 minutes in liquid Tide. 7th Generation recommends cold water for all laundry, but also makes no health claims. Cheer recommends using the hottest water allowed by the clothing label and pre-treating "obvious stains," but makes no health claims.
The US Energy Department and EPA recommend cold water in washing machines except for "oily stains." Perhaps that includes underwear. They have no suggestions on bleach.
An Australian study says allergens are removed from bedding by 5 minutes in "detergent solutions at 25 degrees" Celsius, or 77F. In order to kill dust mites themselves, EPA found that washing in 95F water was not effective, even with bleach and detergent (D. pteronyssinus and E. maynei), but 12 minutes at 127Fdoes kill dust mites. A Connecticut study said an alternative is that 10 minutes in a 105F dryer also kills mites.
Related environmental issues include: How hot can solar water get? all year? Does your detergent identify its ingredients? Are they safe for you? Which ingredients and which types of bleach are removed by sewer treatment and septic systems? If no one is sick and no one has a weak immune system, do you need to kill bacteria in underwear and dish towels? Does drying in the sun kill bacteria? all year?
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