A water timer is a fundamental part of a garden watering system. It's used to automate the daily watering, meaning you don't have to be there to turn your system on and off. This is especially useful for those that lead busy lives, spend long periods of time away from home, or in most cases, just don't want to think about watering the garden.
Battery water timers typically attach directly to a standard garden tap, the ideal place to keep control of your watering system. The batteries for a water timer normally last about 9 months, which is plenty long enough to last an entire growing season. At the beginning of each new season, pop in a fresh set of batteries and you'll be able to forget about it for the rest of the year. Generally you would programme a water timer to turn on twice a day; once in the morning and once in the evening. In our opinion, the Claber water timers are superb and made to a high quality, but the Hozelock water timers are brilliant value for money offering lots of functionality for an excellent price.
If you're setting up a larger system such as a pop up sprinkler system, you may consider using mains powered water timer in conjunction with 24v solenoids instead as these are a more professional choice, and because they're mains powered, do not require any batteries to be changed. A mains powered timer acts as the irrigation controller - the brains of the irrigation system, which then tell the solenoid valves when to activate.