I agree, when you water just water slowly and until the entire media is saturated. You don't want to end up with dry spots in the coir. Check from the bottom to make sure it is draining, but it does take some time for the coir to fully absorb the water (esp. when completely dry). You can't really have a precise measure of how much to water.
Because you are using coir you might want to consider using a Ca/Mg product, if you are using a water source that doesn't have much of a dissolved mineral content.
