What dose it mean by 'run the water'?

I happened to find it while surfing the Net and couldn't make of it.
Please someone tell me what it means by 'run the water' in the context hid below.

[Spoil] คลิกเพื่อดูข้อความที่ซ่อนไว้ He came home. "Wipe your feet!" his wife yelled from the living room. He wiped his feet. "Take off your shoes! Put on your slippers!" she said. He took off his shoes and put on his slippers. "Wash your hands!" she said. He went into the bathroom and washed his hands. "Rinse all the soap off your hands!" she said. He rinsed his hands. He dried his hands on his pants. "Don't dry your hands on your pants!" she said. "Use the towel!" He walked out of the bathroom. "Shut the bathroom door!" she said. He shut the bathroom door. He went to the kitchen to get a glass of water. "Make sure you run the water before you drink it!" she said. He ran the water for about ten seconds. He filled the glass. He drank the water. It was cool and refreshing. "Wash the glass!" his wife yelled.


Thank you in advance.