How much water goes down the drain while you wait for hot

Hot water lives in the heater. The pipe that runs from the heater to your shower is full of water that cooled down since the last time you used it. Open the tap and all of that cold water comes out first and goes straight down the drain. It is not visible waste: it is clean, drinkable water you already paid for that never got used for anything.

The math, plainly

Multiply four things: people in the house, times a day each one opens hot water, liters lost while waiting, and 365 days. For a house of four, two uses a day per person and ten liters per wait, that is 29,200 liters a year. Per person it is the 7,300 liters Hydroloop publishes.

Those ten liters are not a magic number: they depend on pipe diameter and distance to the heater. A bathroom next to the heater might lose three or four liters. A bathroom at the other end of the house, heater on the roof, easily passes twenty.

And the time, which you also pay for

If you wait ninety seconds per use, that same house of four adds up to 73 hours a year standing in front of the shower. Split per person it is the 18 hours listed on the Hydroloop site.

What changes when the water goes back

A hydro-return does not heat faster: it sends the cold water back to the heater instead of throwing it away. The same water loops until hot arrives at the fixture. What used to go down the drain stays in the house.

One common mix-up: this saves water, time and money, not gas. The heater works exactly the same.