How does the water beetle stay underwater for long time?

The Spiders that stay under water for a very long time are called diving bell spiders. They actually make a kind of inverted silken bowl under the surface of the water. They have spines on their body that let them get a bubble of air to stick to them, so they flip their abdomens out of the water and it comes back carrying a bubble or two stuck to it. They then swim to their "diving bell," go inside, and dislodge the air bubble. So they can stay underwater, hunt, etc., for a very long time. Technically, only their abdomens need to go outside the water, so you could argue that they could spend an entire spider lifetime under the surface of a pond.