Residential lawn sprinklers have required backflow preventers that must be tested upon installation by a licensed device tester. Periodic testing keeps drinking water from being contaminated by weed killers, fertilizers or pesticides. Owners may install it in their own sprinkler system or hire a licensed contractor. Permits are required for sprinkler systems and available at the Inspections Department. The cost is $5.00. Solvent cement should not be purple in color and primer shall be purple.