If it tastes bad, maybe there's a reason for that.
(1) As with so many problems, this one can be caused by food. Too much food, food too raw, dirty food, food too ripe, the wrong kind of food and the like. We could go on, but right now, if you have this problem, you don't want to hear any more about going, let alone about gurgling, rumbling, spewing, spraying, trotting, running, doing the two-step, or telltale stains on your pants. Backwater is a sign that your body has something going on that shouldn't be going on, and is trying to get rid of it, and will keep doing that, and that you need to pay attention. Because, really, no one else will want to even think about it.
(2) Where there is water, and it is flowing, or could flow if it wanted to, and there is a channel, then probably there is also a little bit of water in what looks like a sort of appendix stuck onto the main channel. This stuck-on channel probably doesn't have any current at all, and sometimes it is only damp earth, with no real water in it. That's a backwater kind of place, so it's called a backwater. This is where mosquitoes come from, and in-laws.
(3) A resupply town. Nirvana. Metropolis. Civilization. Maybe it's a backwater compared to where you came from, but right now, with you out of food and fuel and looking for a post office and a bed, it's The Big City. Especially if it has pizza and beer, ice cream and beer, or just beer.