catchwater

from The Century Dictionary.

• noun In physical, a conical receiver placed beneath a bulb, flask, or other vessel to catch the water which is condensed upon its outer surface.
• noun Same as catchwork.

from the GNU version of the Collaborative International Dictionary of English.

• noun A ditch or drain for catching water. See catchdrain.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A device which captures surface runoff for use as a water supply.