I think the issue is between people who interpret the statement as "water is predisposed to drain in a particular direction depending on hemisphere" or as "water will drain in a particular direction depending on hemisphere".
Does it have an effect and can it sometimes be seen? Yes. Is it often swamped by other factors and rendered irrelevant? Also yes. That doesn't mean it's false, but it does mean that some statements that rely on it as a factual basis are at best mistaken.
Does it have an effect and can it sometimes be seen? Yes. Is it often swamped by other factors and rendered irrelevant? Also yes. That doesn't mean it's false, but it does mean that some statements that rely on it as a factual basis are at best mistaken.