Don't know about the water issue. It says on the specifications that it's waterproof to IPX7 standards:
Garmin 740 specs.
I'm using one (in a canopied boat) and love it. Livorsi makes a really nice billet bezel for them, too.
I've owned about five different Garmin devices, starting with a small hand-held almost 20 years ago up to 12" chartplotters, and have been happy with both their operation and support.