Treato found 16 discussions about Cold Symptoms and Cats Allergy on the web.
Best Answer: When the toilet is flushed, the toilet is robbing pressure from the shower, which is usually close to the toilet. As the COLD water pressure goes down from the toilet flush, the HOT water pressure is higher, therefore the water gets hotter as the COLD pressure goes down.
What I am getting at is you don't want to turn off the recirculating pump, or the house to warm up, and then get scalded when you turn on your tap water to wash your hands. (for instance, my hot water tank is set to like 130F at it's hottest to eliminate scalds.) Showers are not that hot like that though.