A childhood belief about swimming pools

My grandparents owned an in ground pool in their back yard that me and my cousins loved to play in at a young age. They took great pride in that pool and the garden around it and were determined to keep it clean. In order to do that my grandmother told us that if you peed in the pool the chemicals in the pool would make it turn bright red and everyone would no what you did! All of us believed in this until quite recently!