A shower head is a perforated nozzle that distributes water over solid angle a focal point of use, generally overhead the bather. A shower uses less water than a full immersion in a bath. Some shower heads can be adjusted to spray different patterns of water, such as massage, gentle spray, strong spray, and intermittent pulse or combination modes. Hard water may result in calcium and magnesium deposits clogging the head, reducing the flow and changing the spray pattern. For descaling, various acidic chemicals or brushes can be used or some heads have rubber-like jets that can be manually descaled. A homemade remedy is to immerse it in a solution of water and vinegar for a while, since the vinegar is able to dissolve limescale. Some governments around the world set standards for water usage and regulate shower heads. For example, in the United States, residential and most commercial shower heads must flow no more than 9.5 liters per minute (2.5 gallons per minute) per the Department of Energy ruling 10 CFR 430. Low-flow shower heads, less than or equal 7.6 liters per minute (2.0 gallons per minute), can use water more efficiently by aerating the water stream, altering nozzles through advanced flow principles or by high-speed oscillation of the spray stream. USEPA administers a voluntary water saving program, WaterSense, which can certify low-flow shower heads.