What is the reason why tap water is blue?

1. The residential property is washed with blue disinfection water tank, and the water supply is restored before the disinfection water is put away, and the residual liquid with disinfection water flows to the user's home.

2. Many domestic toilets have blue toilet cleaner or toilet cleaner in their water tanks, but most of them have no backflow preventer. Once the water is stopped, negative pressure will be generated in the tap water pipeline, and the blue solution in the water tank will flow back into the tap water pipeline. When the water supply is restored, blue water will flow from the faucet.