I get the impression, sometimes, that everyone knows this stuff but me and I’m making these huge discoveries. But someone somewhere out there doesn’t know this, so here you go —
I know most people don’t have water filters. We here in Podunk are blessed with really nasty water that comes from our wells. The water is great — it’s all the rocks and iron and clay that’s in it that makes it nasty. But, I must say, considering what city folks have in their water, and what it smells like, I’ll take my little rocks any day of the week.
But I have to change the water filter once a week or so and I really hate that job. Mostly because the filter is in the closet with the water heater and I’m always afraid something’s going to jump out at me when I open that door. Nothing every has, but that doesn’t mean they aren’t just waiting for the perfect opportunity. It’s nice and warm and dark in there. I can think of a whole list of critters who would love to live there. Well, except for the poison that’s thoughtfully provided for them. 
Okay, so when I change the water filter, I have to turn off the water to the house, of course, and then release the vacuum and wait for the water in the filter housing to drain out so I can open that up without it leaking all over the place. I used to set the timer for 15 minutes or so, but it never failed that at least every other time I did this, I wouldn’t hear the timer, or I’d get distracted by something else and not remember that I was in the middle of that job until I wanted to use the water — which is off, of course — to fix dinner or take a shower. Oops!
I don’t know why, but one day I flushed the toilet. Well, I probably do know why, and you probably do, too. I probably had to go potty after I started the filter-changing process! But, anyway, that drained the lines! Woo hoo!!!
Shut off the water — leave the faucets open — flush the toilet — change the filter! The water’s drained before I can even get back to the hot water heater closet to take out the dealie.
So, there you go. One of these days, this information is going to be important to you.
