The short version: there's no guarantee the water that comes out of any tap is free of bacteria, so you have to boil your water before you use it to kill anything that could be there yourself. You can still shower and wash your clothes, and theoretically you can wash dishes still (though I personally feel ick doing that), but if the water is going to go in your mouth it's gotta be bottled or boiled and cooled. It's an inconvenience, but it's not the end of the world.
But then you realize the coffee machines at work have in-line water systems so you can't use those and there's no coffee. And the water coolers were disposed of a few months ago in favor of an in-line filtration system to save on plastic so now you can't use that. And restaurants can't possibly boil all their water before using it to cook or make drinks or even ice so then those are closed while they wait for the advisory to lift. And you have been diligent and boiled your water and used it for drinking and cooking but forget like an idiot to use it to brush your teeth like somebody you all know (*cough*me*cough*).
The number of times you just...use water without really thinking about it is staggering. It's easy to remember to use your boiled water for those conscious choices, but all the times you're just going to flip on the faucet real quick in passing to rinse your hand or wet your toothbrush or grab a few ice cubes for your drink? That's what gets you.
Have you ever had to follow a water-boil advisory before? How long did you have to do it?