purple water
n.— «An alternative to using gray water is treating it with a home sanitizer system to create what’s known as “purple water.” While it’s not safe enough to drink, purple water is considered safe enough for use on lawns, golf courses and irrigation in other states.» —“Scientist sees gray water risk” by Benjamin Price Athens Banner-Herald (Georgia) Nov. 25, 2007. (source: Double-Tongued Dictionary)
Further reading
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FWIW, purple is the color used to identify recycled water pipe. while i know purple water shouldn’t(?) kill me, on a hot summer day i will check to see if the lawn water is spraying out of a purple sprinkler head before driving in.