Okay so here's what I do with my water bottles, y'all, bc your tags are concerning me.
First, these are the water bottles I use. Dishwasher safe, and kept water cold for an entire 8h drive. A little spendy but I bought 2 like... 3 years ago and I probably won't replace them for a really really long time bc they're metal.
I hate water bottles with straws, but my family uses some. It's easier to keep them clean if you use the spout style, but in either case:
Get a straw brush. They're very cheap. Brush out your straw with soap and then put it in the dishwasher with the rest, in the silverware bit so it's sitting up vertical and the water can get in it. The very hot dishwasher water plus you actually cleaning it out with a brush FIRST to loosen up anything sticking inside = best.
Check your bottle when it comes out of the dishwasher; every so often you may get a little schmutz in there from the fact that the bottles hip in a little at the top. It'll come out with a rinse.
Once a week or so, put a couple teaspoons of vinegar in a couple of cups of hot water, enough to submerge the lid fully. Take the ring out of the lid, submerge the lid, let it sit for 20m. Brush the lid out really good. Reassemble it and run it through the dishwasher - or wash it really well by hand. (Except for the dishwasher bit, this is also how to clean CPAP parts.) You can use rice, white, apple cider, the vinegar type doesn't really matter - you just want to make the water acidic so it helps kill the mold and anything else gross growing in there.
Reusable water bottles are wonderful. I love my metal bottles and I probably won't have to buy another bottle for the rest of my life. I might have to replace the top once or twice.
Please keep them clean and don't make yourselves sick.