Barrel for collecting rain water to provide irrigation at a future date.
Rain barrels collect rainwater (typically from a building's gutter system) to be used at a future date for irrigation. Such systems typically feed drip irrigation systems, or a tap for hand watering (e.g. via hosepipe or watering can) because a typical barrel can only hold a limited volume of water.
Rain barrels are very useful in drier parts of the world where they can be used to water plant pots and smaller areas during drought restrictions; and are even used in wet temperate areas (e.g. the UK) where a barrel or two can keep a garden green during the height of summer.