How to Shut off Water Supply
Do not panic. Seriously, the water won’t drown you. You have maybe 10 seconds of spray before pressure drops. You are faster than a broken pipe.
3 Ways to Turn Off Your Water Supply Quick and Easy - wikiHow
Do not use a wrench on the main valve unless it’s stuck. Turn it by hand first. Over-tightening can crack the brass. Then you’ll really have a problem.
And please, do not forget which way to turn. I know “righty-tighty” feels basic, but under stress, your brain goes blank. Remember: clockwise = off. Write it on the wall with a Sharpie if you have to. I’m not kidding.