Another clear law is the one that says you must not start the game if any part of the ground is unsafe. If we've going to be inflexible on clear laws, then the game simply doesn't go ahead if there's a bit of ground where you need to blow up for safety.
OK but that's a Law you have worked around with agreement of skippers. It's a not an on-field gotcha.
The pre-game disucssion could have extended further -- with captains
'Gentlement - if a loose ball ends up in the puddle and stops, then as referee I will stop the game as we've agreed its unsafe. BUT THEN what shall we do about restarts : would you like me to decide what would have happened if the puddle wasn't there and restart accordingly ? Or should we restart with a scrum as per normal for 'any other stoppage'.
If they had gone for the 'decide what would have happened option' then fine. I bet they would have said you what? No, a scrum of course, as that is the reasonable expectation. I don't think a a ref should invent Laws on the fly.