system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:where does water actually come from and where does it go before it reaches my sink?
gpt
Just handling the "last lap" part of it, the part where it enters and leaves your sink, the answer depends on just how rural you are.

**Cities and Suburbs:**

* Where it comes from: usually a nearby river or lake. The water company (or water department) pulls water from the river or lake, filters and cleans it, and pumps it into big pipes that criss-cross the city and surrounding areas (water mains). There's a smaller pipe that runs from the nearest water main to your house, and then smaller pipes that run from there to the sink.

* Where it goes: through a small pipe to a vertical, larger pipe (standpipe) that makes a right-angle turn under your basement floor (usually) and runs out to the sewer main. From there it runs downhill to the sewer treatment plant which filters as much as they can out of it, and pumps the rest back into some river or lake; usually the same one, usually down-stream.

**Outer suburbs and rural:**

* Where it comes from: the pipe runs from your house to a well, which is a pump connected to a deep pipe that runs down to where the ground is so wet that, if you dig a hole, water seeps out (the water table). That layer of water-soaked ground has been there for a very long time; some of that water seeps in from nearby rivers or streams or lakes, but most of it was there when the ground formed and will be gone when it's used up.

* Where it goes: from your sink, it runs via pipes out to a holding tank in your back yard (septic tank). The solids settle out and have to be shoveled out every so many years. The water slowly seeps through the sides of the tank into the ground.