The phrase for "及时关掉水龙头" in Engpsh is "turn off the tap promptly".

The phrase comes from the practice of conserving water by turning off the tap promptly after use, instead of letting it run continuously.

Examples:

Remember to turn off the tap promptly when you're done brushing your teeth.
It's important to turn off the tap promptly to save water.

中文翻译：

记得刷牙完后及时关掉水龙头。
及时关掉水龙头以节约用水是很重要的。