SEA-NRT is almost entirely over water. It may help that part of the "water" is frozen. But land isn't far from the routing (not for instance like the Hawaii and Oz flights).

If you're going to India transpacific, you'll probably be connecting via BKK or SIN. In that event, you'll likely be crossing the Bay of Bengal. Now that's a body of water best avoided, especially during the monsoon season. I've had some nasty surprises before.

The alternative as many suggest, is to go transatlantic, in which case you'll encounter less water. Europe/AMS to India is mostly over land (depending on where in India you're flying to).

The AC flight YYZ-DEL follows a northern but transatlantic routing, so although in theory it looks like it's flying over Siberia, in practice it's further to the south.