That’s not something I’d worry about myself. Best to keep water out, but a single drop, life’s too short to worry about that. IMO anyway. Brake fluid is usually alcohol based, so attracts water like rice attracts white. So by its nature it gets a little water in it every time you open the system anyway, like when you open the cap to see how much fluid remains. From the water vapor in the air. And probably some water gets past the seals over time. So all in all you got an extra drop to begin with. An imperfect world, but I expect you got more things to worry about than that.
If you want to worry, worry about someone accidentally finding and using the turkey baster for preparing thanksgiving dinner. That would be a very bad thing to happen. Suggest to mark it “for garage use only”.