The short answer
Because the hot water has to push all the cooled water out of the pipe first, and that takes more water than the pipe holds. Research collected by the American Council for an Energy-Efficient Economy puts it at 10% to 100% more than the volume of the pipe. In a big Northern Virginia house with the water heater in the basement and the main bath two floors up, that’s a real amount of water, every shower.
The part most people don’t know
You paid to heat that water. It sat in the pipe after the last person used it, cooled to room temperature, and now it goes down the drain while you wait with your hand under the faucet. The same ACEEE paper cites research that up to 30% of the water used for showering is wasted before anyone steps in.
Why more than the pipe holds? At the low flow of a modern showerhead or faucet, the first hot water mixes with the cold water ahead of it and gives up its heat to the cold copper. You get lukewarm water for a while before you get hot, and you run it until it’s actually hot.
$99 Water Heater Flush
We drain and flush the tank, check the anode rod and test the relief valve, then go through the house's plumbing with photos, included. See the flush
Want your own number before anyone comes out? The water heater estimator prices your house in a few questions.
Do the math on your own house
Swipe to see all columns →
Swipe to see all columns →
| Pipe from the water heater | Water it holds | What you run before it’s hot |
|---|---|---|
| 50 feet of 1/2 inch copper | About 0.6 gallons | About 0.7 to 1.2 gallons |
| 50 feet of 3/4 inch copper | About 1.3 gallons | About 1.4 to 2.5 gallons |
| 100 feet of 3/4 inch copper | About 2.5 gallons | About 2.8 to 5 gallons |
Pipe volumes are standard copper sizes. The last column adds the 10% to 100% from the research. A run of 100 feet isn’t unusual in a large house once the pipe climbs two floors and crosses to the far side.
Why it gets worse in winter
In winter the pipes in the basement, the crawl space and the outside walls sit colder, so the hot water loses more heat on the way and the wait gets longer. The water coming into the house is colder too, which is also why hot water runs out faster in winter. If the wait got longer all at once, or the water never gets fully hot, look at the water heater: our no hot water checklist covers the common causes.
What actually fixes it
- Insulate the hot water pipes you can reach in the basement or crawl space. The water stays warm longer between uses, so the next wait is shorter.
- An on-demand recirculation pump sends the cooled water in the pipe back to the water heater when you press a button or walk into the bathroom, so it doesn’t go down the drain. A pump that runs around the clock keeps the pipe hot all day, and you pay to keep it hot.
- A shorter run. When a bathroom gets remodeled or a water heater gets replaced, it’s the time to look at where the hot water line goes.
A tankless water heater doesn’t fix the wait. It still has to send hot water through the same pipe, and it takes a few seconds to fire up first. Our tank vs tankless guide covers what tankless does well.
The other water heater fact most people miss
If your water heater is electric, a heat pump model uses at least 70% less energy than a standard electric tank, according to ENERGY STAR, which puts the savings at about $600 a year for a family of four. It works like a small heat pump on top of the tank, pulling heat out of the air around it. Our heat pump water heater guide covers the Dominion rebate and where one fits in a Northern Virginia basement.
Have a plumber look
If the wait got worse, or the water heater is getting old (our water heater life span guide has the numbers), the water heater flush is $99: we drain and flush the tank, check the anode rod and test the relief valve, then go through the house’s plumbing with photos, included. The photos show you the pipe runs and the tank in one visit. If the tank is the problem, our water heater estimator shows your installed price first, then $500 comes off a new water heater, any size, replaced by our own plumbers.
Book it
Book the water heater flush, call (703) 997-9757, or book online from goswiftpro.com/cookiesoffer and a box of warm cookies comes with the visit. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
Why does it take so long for hot water to reach my shower?
The hot water has to push out all the water that cooled in the pipe since the last use. Research collected by ACEEE found that takes 10% to 100% more water than the pipe holds, because the first hot water mixes with the cold and loses heat to the pipe.
How much water is wasted waiting for hot water?
It depends on the length and size of the pipe. Fifty feet of 3/4 inch copper holds about 1.3 gallons, so you run about 1.4 to 2.5 gallons before it’s hot. Research cited by ACEEE puts it at up to 30% of the water used for showering.
Does a hot water recirculation pump save water?
Yes. It sends the cooled water back to the water heater instead of down the drain. An on-demand pump that runs only when you need it saves the most energy. One that runs all day keeps the pipe hot around the clock.
Will a tankless water heater get hot water to the faucet faster?
No. It still sends hot water through the same pipe, and it takes a few seconds to fire up first.
Why does hot water take longer in winter?
The pipes in the basement, crawl space and outside walls are colder, so the hot water loses more heat on the way. The water coming into the house is colder too.
