Reddish water
Wai is fresh water and mea here is a reddish brown. The name describes streams running red with eroded soil, and it is applied wherever that happens — there is a Waimea on Kauaʻi, one on Hawaiʻi Island, and Waimea Bay on Oʻahu.
The Hawaiʻi Island town is also called Kamuela, the Hawaiian form of Samuel, after Samuel Parker of Parker Ranch. The second name exists mainly so the post office can tell the Waimeas apart.
Waimea Canyon
The Kauaʻi Waimea sits at the mouth of Waimea Canyon, cut by the river through red volcanic rock — the colour that gives the name. It was also where Captain Cook first landed in the islands, in January 1778.