I worried when my entire motor was completely submerged in dirty water, during a sudden thunderstorm downpour recently - the water level was above both pedals for over 15 seconds. Standing on the pedals on max PAS, my bike created a small bow wave as it pushed through and out of this small pond, which had suddenly appeared in the road.... but I had covered all of the plastic connectors with self-amalgamating tape when installing, I think that helped. Without max PAS, I would've just toppled over. While drying the bike next to a hot radiator for several hours, a small amount of water drained out of the bbs01b motor casing... and the bike seems completely fine thus far, a couple of weeks on. Using it after a good drying, heats and expels moisture from the motor, I think, but might kill the electrics (wiser comments above), if water's in the controller, which I'll never know unless I take the motor apart to look at it, which might make the motor less waterproof - but there are no worrying noises, therefore I'll continue ebiking till something stops working. Reading these forums, i seems the bbs01b are weatherproofed pretty well, I bloody well hope so.
Cycling, work, I'm often rained on - can't avoid it. I've got two rucksack rain covers velcroed over the battery - seamless "Waterproof" material, two in case one is rubbish. Cheap covers like that are not waterproof for long after a couple of hours of sustained rain... could further waterproof them using Nikwax spray or something. Of course, they won't stop water ingress from beneath the battery holder... My rain hat over the display is a clear poly bag, gaffa taped on permanently. The throttle is shielded from rain by a navigation cellphone case, which acts as a roof.
Clearly what I really need is a giant umbrella over the bike held by a flock of drones, which leads to more waterproofing and power conundrums...