It depends on the Plumbing in your building, but in the States its usually as clean as what comes out of your kitchen faucet.
I am not sure about gas or oil. A foul odor could be from the sewer system. All of the drains in your home have a trap that keeps water in the pipe. This water prevents sewer gases from coming into the home. If you pour water into each drain (sinks, tub, shower, toilet, and any other drain in the home), you may find that the smell goes away.
A water shortage that goes on for several years is referred to as a water crisis.
the swimer
Light
basically it evaporates into the sky, eventually becoming rain/snow and falls back to earth. It rises into the atmosphere.
because before it touches the water or goes under water u can smell it. or maybe underwater the poop has farts
the reason why the toilet makes noise when you turn water on is because all the water lines are conected so when you turn on water the toilet gets affected and the water that goes down a drain goes to the water pipe.
clean water is naturally dirty, it goes through a process in which then it becomes clean.
the water will become dirty
It all goes to the same treatment plant and is sent down stream to the next town or city. All tap water is the same, sink or toilet.
All waste water travels to a water treatment site through underground pipes and is filtered clean before being released.
Goes straight to sewer
Sometimes the water hit parts of the glaciers that would get it dirty. The water is also dirty because there is dirt and thins fall into the water that is dirty. Or maybe when the rocks under the snow goes down the hill it leaves the dirt behind.
Under what circumstance? New toilet, when you turn the water on, water goes down the overflow tube to fill the bowl. You don't have to flush it the first time to fill the bowl.
If the electricity for the water power plant goes out, water cannot be pumped to your toilet for flushing.
I personally think the sewer line also your toilet water goes there.
That there either one curious or your not giving them enough water.