Almost all plastic release chemicals having estrogenic activity [1] so not be default harmful, but probably harmful.
It's also worth noting that consuming microplastics doesn't result in them being bathed in water, but rather our acidic digestive tract designed specifically for leaching chemicals out of things.
Disclosure: Involved in a project to raise awareness about plastic and noise pollution in the water [1].
[0]: https://thinkprogress.org/zooplankton-are-eating-plastic-and...
Your general point stands though: the particular water based solution in question serves a particularly important purpose!
Even better, you could put your plastic where your mouth is and try a diet of washed microplastics every meal to see how it affects you. It’s not immoral if you do it to yourself!