Which is more wasteful? Running tap water to warm it before boiling, or starting with cold tap water?

Question

Please help settle an argument I'm having with my husband. He insists on running the tap for several minutes until the water gets warm, then filling the pan and setting it on to boil. He says it wastes less energy to start off with warm water, since it takes less time to boil. While this is probably true, I think it's worse to waste so much water and negates any environmental benefit we achieve with the energy savings. Certainly we can come up with other solutions (i.e. watering plants with the excess water that comes out before the tap water gets warm) but from a purely scientific standpoint, which of the aforementioned scenarios is better or worse? We've got dinner riding on this. Thanks!

Answer 1

I have wondered about this myself....and I think that here in the northeast when its cold outside that the water from the heater to the pipes must have to leave the water heater hot, travel to the tap, but also hot water fills the pipes all the way back to the heater....so when I turn off the tap that hot water sits in the pipes and cools down...such a waste!
So my solution is to use cool water to fill a pot to boil, but if I am planning to have the hot water run for awhile, like in a shower or doing dishes, then I let it warm up.

I hope a scientist answers this. I want to know too!

Answer 2

The science.

Energy use:

Depends on how your tap water is heated.

If you have a solar hot water system, then running the tap to warm makes perfect sense, as the water has been heated using the suns energy.

If you have a small electric boiler or a gas system, then your husband is still likely correct as these vessels are purposely designed to heat water as efficiently as possible using. A cooker and saucepan is not.

Gas heating is generally more eco-friendly than electric, as it consumes the fuel it uses at source (i.e. at your cooker), rather than in a power station where a significant part of it is lost in the process of it reaching you, so if you have an electric boiler and a gas cooker, there probably isn't much to choose.

Water use:

Obviously running the tap wastes water, and as you rightly point out, that water can be recycled.

Conclusion.

Personally, I would run the water hot.

*edit looking over previous posts*
Insulated pipes will make some difference as you will need to run off more water to get hot coming through, and your system will reheat this same water, but by the same token you still have to heat up your pan.

Microwaves are very good in that they heat up only the water you plan to use, but they are not especially efficient compared to other methods when you need a fair amount of water (more than a cup of coffee's worth)

The guy who said only heat what you need to use is spot on. In most households, much more energy would be saved by doing just this, than worrying about whether to run the water hot.

Answer 3

If you have to run a lot of water to warm it up then 1. You are wasting all that fresh water down the drain, 2. Hot water ain't free just because it comes out of the tap, the hot water heater has to use more energy to warm the tank back up again, and 3. Using only the amount of water and energy required to make a cup of tea will always be the most efficient; running the water until it gets hot just to heat it AGAIN is a waste.

And gas stoves may be cheaper than electric bt they are NOT more efficient. If they were the kitchen wouldn't get so hot when using a gas stove.

Answer 4

This situation has several things to consider besides who is correct. Cold water in a hot water line (early in the morning) has been sitting in the copper pipe for hours. The old copper joints used lead in their fabrication. Some of it could be touching the water. If you use that water for drinking you are getting more lead into your body. waiting until the warm or hot water comes thru is safer over the long run. Right? Wrong! All hot water tanks has zinc rods to reduce electrolysis. The large pieces collects on the bottom of the hot water tank as silt, the smaller ones comes out the faucet.. Some of it may get into that coffee pot. and into your soup. Better if you use cold water for making coffee, but make sure you flush your toilet and brush your teeth before you make that pot of coffee. Now take that plumber out to dinner.

Answer 5

If you're water heater doesn't emit CO2 it wouldn't matter (it would just be about which is cheapest) and that is possible if you've got a solar water heater on your roof or an electric water heater running off a mostly nuclear electricity grid.

Although I suspect you don't have either of them in which case you'd probably be better off just using extra energy to warm up cold water although that depends a lot on the efficiency of your water heater compared to your stove (I suspect that your stove wastes more energy).

Answer 6

well for me --- i think it depends on your situation. Do you live in town or a city, or are you on well water, do have gravity fed water supply or an electric booster pump. Do you even hace electricity or are you on solar? or battery back up or generator or ..... do you have Renai always hot water heater?
and I am sure there are even more scenarios.

My best answer would be if you have been using warm water and it's quick to be warm out of the tap -- then use the warmest you can, then use whichever is cheaper to warm it for you -- is the stove cheaper or is the microwave cheaper?

If the water is running very cold -- i just put it in the "nuke" and warm it, or just turn the kettle on the stove on.

I am on generator right now -- in the process of installing solar and battery back up.
We have no electricity unless generator is on, all water is gravity fed pressure flow.

i just have a thing about the water running - and running and running too, grrrrrrrrrrrrrrrrr to too much water just wating down the drain. if you are in a city -- i would use the nuke -- warm in glass or microwave ware for this -- no plastics or anything

Answer 7

Try this.....

Use cold water and heat it in the microwave. You save water, money, and time. Even if you have to heat the water for cooking....say pasta...heat it first in the microwave. The you start with boiling water in about 2-3min.

Also, I've heard(dont know if this is true) that hot water from the tap should not be used for cooking/drinking because of all the impurities that is picked up in the pipe because of the heat of the water.

just my thoughts

Answer 8

The problem isn't microbes-it's lead. If you have an older house the hot water can dissolve lead from the pipes. Boiling the water only increases the concentration. If you have a newer house it's safe. Also, lead is mostly dangerous with long term repeated exposure, so once or twice shouldn't be too risky.

Answer 9

you husband must be rich. you pay for wasting all that unused water going down the drain and you pay again to have all that unused water to be processed by the sewage plant. then you pay to reheat the same amount of water he ran down the drain that is replaced in the hot water heater.
if you want instant hot water at the faucet go to Home Depot or Lowes, get a recirculating valve and install it. it keeps hot water at your faucet instead of running it for 10 minutes waiting for it to get from the heater to the faucet.
I also like the idea suggested of nuking it. 90 sec has a cup of water very hot for a cup of tea. Corning ware qt bowl I use for 3 minutes(any longer and it boils over) for a can of corn/beans instead of firing up the stove, bringing it up to tempature, and warming dinner(time it sometime-you do the math).
those are my thoughts on the matter.
john

Answer 10

If the warm tap water comes from your gas heater, it will cost you the same energy to heat up water, as with a gas heated stove. Electrical stoves use more energy, because they are less efficient. You are right, that running tap water, until it gets warm is a complete waste and for the purpose of getting warm water to heat it up further on the stove it makes no sense, since you not only fill up your pot, but have to fill up your entire warm water pipe (from the heater to the faucet), before you get warm water. Reminds me of my wife's girlfriend, who buys clothes, because they are on sale, but don't fit her.
You can take it to the bank, that you use more energy, getting warm water from your faucet for a little pot, because you lose most likely 4-6 times as much heating up your pipes. That said, you could get one of this warm water heating pots with its own electrical coil, which is very direct and efficient, to preheat the water to boiling point.
Here are some tips to conserve energy:
1. Always put a cover on a pot, you heat stuff in. As tighter the cover, as quicker you heat and as less energy you use.
2. Water can not get hotter then boiling temperature. So, after your water boils, lets say for spaghetti or eggs, you can turn the heat down considerably, the pot with a cover on will keep boiling.
3. A gas stove is more efficent then a electric stove.
4. For your warm water heater, turn your heat down to maybe 80 Degrees Fahrenheit, just enough to get a comfortable shower. As higher your heater has to heat, as more energy is wasted.