Water damage

No iphone is waterproof.

Water resistance will keep water out of 99% of phones but it is not permanent and damage is not covered by standard warranty, (only by AppleCare+)

Back it up daily as it could die at any time

It's a limited water resistance when fresh from the factory. I suppose it's better than not trying to be water resistant, but it's not like a diving watch. They use adhesive seals that are more like tape. They degrade over time and especially when they're exposed to water or extreme temperatures. I would never rely on the water resistance.

Because I rely on my iPhone8 as a hotspot between houses, I purchased a LifeProof brand full-enclosure case ... claimed to be waterproof, drop-damage resistant, etc. Also because at the time the smooth rounded case was not as secure a grip as my old flip-phone. Pricey at $90, but purchased because LifeProoof said they cover damage if it fails.

Not that I have had any claims on it, so cannot guarantee their actions.

There is also the SIM tray and the mute switch, not to mention the lightning port and the speakers. I tape over the mute switch and SIM tray and if I had wireless charging I would ytape over the lightning port too. AppleCAre+ is a good idea too - anything to reduce the risk of replacing the phone entirely as water damage is not repairable.

Cases themselves carry the risk of holding water close to the seals, so taking it out of a case until both are dry is advised after a water incident.

But best advice is not to get it wet or subject it to trauma, and carrying a phone while sledding poses both risks.

Good point about "cases hold water". Safety assumes the case truly is waterproof. Do not blindly believe me, but consider the risks as I must.