Why add acid to water when diluting?

Whether you add acid to the water or water to the acid is one of those things I know it's important to remember, but always have to puzzle out. Sulfuric acid (H2SO4) reacts very vigorously with water, in a highly exothermic reaction. If you add water to concentrated sulfuric acid, it can boil and spit and you may get a nasty acid burn.

If you spill some sulfuric acid on your skin, you want to wash it off with copious amounts of running cold water as soon as possible. Water is less dense than sulfuric acid, so if you pour water on the acid, the reaction occurs on top of the liquid. If you add the acid to the water, it sinks and any wild and crazy reactions have to get through the water or beaker to get to you.