Poly(vinyl alcohol) (PVA) precipitates in many kinds of aqueous salt solutions. While sodium sulfate, a coagulant for PVA fiber, precipitates PVA to yield a white rigid gel, coagulation of PVA with aluminum sulfate, a coagulant for water treatment, yields a slime-like viscoelastic fluid. One type of homemade slime is prepared under basic conditions with borate. The method reported in this paper is carried out under acidic conditions with materials that are used for water treatment. Through this demonstration, students can learn about chemical interactions through the coagulation and diffusion of slime. This demonstration can be carried out in 30 min.