Full Idea
If a cupful of dirty water is mixed evenly with a ton of earth, no dirty water remains, and the same goes if we mix it evenly with a lake of clean water.
Gist of Idea
Mixtures disappear if nearly all of the mixture is one ingredient
Source
Peter Simons (Parts [1987], 6.2)
Book Reference
Simons,Peter: 'Parts: a Study in Ontology' [OUP 1987], p.219
A Reaction
This means that a mixture is a vague entity, subject to the sorites paradox. If the dirt was cyanide, we would consider the water to be polluted by it down to a much lower level.