A standard garden hose can use 10 gallons per minute or more. This means you can easily use 100 gallons of water with only a 10 minute car or pavement wash.
A broom, on the other hand, uses no water and gets the driveway and sidewalk just as clean.
If you must hose down pavements or wash your car, be sure to attach a shutoff hose nozzle (such as the one shown in Figure 1) on your garden hose. A good quality hose nozzle should not leak or drip when in the off position. Check to make sure that your hose is not leaking at the hose bib connection either. A hose washer will usually take care of hose bib leaks.