It's not about the water inside, it's about the plastic. I do the same as grandparent, refill disposable but sturdy bottles, I change every 6 month or so. I ass

It's not about the water inside, it's about the plastic. I do the same as grandparent, refill disposable but sturdy bottles, I change every 6 month or so. I assume the plastic itself is shedding particles away more and more as it ages. There is a bad smell that develops after a few months. Probably from bacteria build up.