Water, mostly trapped in sedimentary rocks, lubricates the tectonics plates, by lowering the melting point of the rocks. Without water, on a earth-sized planet, you get geology like Venus, which doesn't have tectonic plates. Instead, every few hundred million years, the internal pressures build up enough the volcanos erupt everywhere, resurfacing the entire planet.
With a little water, you won't get anything quite that dramatic, but there will be bigger earthquakes at the ocean trenches and fewer volcanos along the mountain chains neighbouring them. The hotspot volcanos will be bigger, since the plates will be moving more slowly.
With a little water, you won't get anything quite that dramatic, but there will be bigger earthquakes at the ocean trenches and fewer volcanos along the mountain chains neighbouring them. The hotspot volcanos will be bigger, since the plates will be moving more slowly.