Witchwater (or "witch-water" or "witch water") is a phenomenon that occurs on asphalt roads during bright cloudless days, wherein sun-lit objects (vehicles, telephone poles, trees, etc) that reside on or near the road create inverted reflections in the road beneath/behind them when viewed from a long distance, due to the still-shiny/smooth "vertical" portion of the porous pavement's asphalt-particles that lie just beneath the actual upper-surface (horizontal) portion of the particles that have become soiled and dulled by dust and drying. From the low line-of-sight angle that is achieved when viewing the road at a distance, these tiny facets of glossy and cleaner asphalt form a mosaic of mirror-like surfaces that reflect objects passing a short distance above them, and thus make the road's dry surface appear to be wet and shiny.
Because this reflected image always "vanishes" when one gets closer to the area where the reflection had previously been visible from a greater distance, the phenomenon has been humorously nicknamed "witchwater", in that the seemingly wet/reflective area on the pavement seems to disappear as if by magic, or as if witches had cast a spell on the road's surface to fool passing motorists or pedestrians into thinking there was water on the road, when in fact there was not, similar to a desert's mirage of a non-existant oasis. This phenomenon is especially commonly seen to occur on major highways like interstates where there is more frequent resurfacing of the asphalt, and so the tarred material is often more fresh and glossy than the surfaces of older, less-travelled secondary roads that are consequently less-frequently serviced with new hot-top. Warmer temperatures increase the reflective effect, also, as the heated road causes the solvent-oils in the asphalt to come to the surface of the particles of tar, enhancing their reflective properties.
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