The gardener who can do a thorough job of watering with hose in hand is rare indeed.
Assuming that the hose spews out about 3 gallons per minute in a circle about 4 feet in diameter, I roughly calculate that said gardener would have to stand immobile for more than two minutes before moving on to the next 4-foot-in-diameter circle of thirsty plants. Pretty boring, if you've got a whole vegetable or flower garden to water.
A sprinkler is one obvious solution.
Even better is "drip irrigation," a method of applying water to plants slowly and over an extended period of time. Drip irrigation has many benefits, not the least of which is cutting down water use by about 60 percent.
A primitive drip irrigation system could be cobbled together by running water through an old garden hose that's riddled with holes along its length and has its end plugged. The problem is that less water would drip from the holes at the end than from the ones at the beginning, and higher ground would get less water than lower ground.
A drip irrigation system you purchase has water emitters engineered to offer a consistent, specified output over wide changes in elevation and pressure. They're also made to be resistant to clogging or root penetration. You can buy tubing with emitters installed, say, 6, 12 or 18 inches apart; such tubing is good for watering whole beds. Or you can buy solid plastic tubing and punch in emitters wherever you want.
Emitters, those you plug in or those pre-installed, typically put out water at a specified, leisurely rate of 1/4 to 4 gallons per hour.
For a flower bed or closely spaced plants like carrots, tubing with emitters already installed wets the whole bed. Capillary attraction into small pores in the soil draw water sideways even as gravity is pulling water downwards, so wetted areas within the soil overlap.
Water's lateral spread depends on soil type, from about a foot in sandy soils to about 3 feet in clays. So in a bed, these dripper lines could be laid out a couple of feet or 6 feet apart, depending on whether the soil is, respectively, a sand or a clay. Soils are rarely pure sand or pure clay, so actual spacing lies somewhere in between.
For individual plants like widely spaced small shrubs and trees, figure on using solid tubing with one or more emitters next to each plant. Emitters that attach to the ends of thin flexible tubes are useful for watering plants in pots.
With emitters, tubes and a connecting hose in place, we are back at the hose spigot. Before a connection is made to the spigot, a pressure reducer and filter are needed. The pressure reducer drops the pressure to about 10 psi, which is all a drip system needs, and dispenses with the need for any high pressure fittings. And a 200-micron filter further reduces the chances of any clogging.
Right at the hose spigot is the best part of a drip irrigation system: the battery-operated timer. This timer automatically turns the water on and off, and at about the rate that garden plants are using water.
Of course, water use depends on the weather and the size and kind of plants, but a half hour of dripping per day is usually about right. If a timer can turn the water on and off three times a day, set if for three 10-minute waterings; if six times a day, set it for six 5-minute waterings; etc.