Exactly. Your used toothbrush sitting wet in your bathroom is full of fecal matter.

Which can be mitigated significantly, if desired, by using bleach tablets in the toilet tank. That has knock-on consequences, but they are manageable.

I think microplastics are more likely to kill me before the fecal matter in my toothbrush.

I thought microplastics are still more of a hypothetical health hazard than a proven one?

In any case I don't think there is any need to choose one over the other.

Not everyone, I live in a victorian house with a separated shitter.

That's common in contemporary houses as well.

Bonus points if you teach your kids not to drink the water.

Probably better for their immune system in the long run.