Take the 2-minute tour ×
Skeptics Stack Exchange is a question and answer site for scientific skepticism. It's 100% free, no registration required.

I have heard many times during "Save water" campaigns that bathing using a shower uses more water than using a bucket or bath-tub? Is this true?

share|improve this question
18  
This is easily calculated at home: take a bucket of known capacity, turn on the shower, use stopwatch to measure how long it takes to fill the container. Compare this value to the time length of your average shower. Use your container to fill a bathtub to the level you would normally for taking a bath. Count the number of containers used to get to that water level. –  horatio Apr 14 '11 at 16:59
    
Depends how long your showers are and how deep you like the water to be when you bathe, and how much effort you want to spend bathing. You could save even more water by using a bowl of water and a sponge, but it would take much longer to get clean that way than I would like. –  Peter Olson Apr 14 '11 at 17:06
3  
In Finland it's commonly suggested to specifically take showers instead of baths to save water (I have sources in Finnish). I'm quite surprised at your question. Could you cite some such campaigns? –  dancek Apr 14 '11 at 21:43
1  
@horatio : the people from the "Save water" campaigns wouldn't like to hear that :). –  djerry Apr 15 '11 at 7:11
5  
This was deleted as an answer, so I'll put it here as a comment since I think it may help you get what your are looking for: Impossible to answer as it depends on how long of a shower you take, whether you turn off the water while scrubbing, how full you get the bathtub, etc. If you really want to know if it saves YOU water and assuming you have the normal shower/tub combo, just do this. Next time you take a shower, put the drain plug in. When you are done, see how full your bathtub is. –  Kevin Apr 15 '11 at 15:27
show 4 more comments

2 Answers

up vote 10 down vote accepted

A bath tub has a capacity of around 110L.

An average 80kg person has a density of 1010kg/m3, therefore a volume of 0.08m3 or 80L. Let's say the person is only 50% under water when taking a bath.

That means around 70L of water are poured in the bath tub so that it's full to the rim when one person is sitting in it.

Compare with a shower. A typical shower would take around 10 minutes and shower heads have a water flow ranging from 6 to 16L per minute or 60L (water-saving shower heads) to 160L (normal shower heads) of water per 10m shower.

In practice, water saving showers are equivalent to baths, whereas normal showers use up to 2.5 times the water with respect to baths.

share|improve this answer
    
A bathtub of 110 liters is quite small, the most I've seen have been 150-160 liters. Also, I think the water flow values are the maximum possible with a shower head. I, for one, don't fully open the tap unless filling something. –  dancek Apr 14 '11 at 21:38
6  
Here in Australia, after all the droughts, we've gotten used to 4 minute showers - which is another point. You more or less need to fill up the tub to have a bath, but you can cut down on the length of a shower. –  Jivlain Apr 15 '11 at 14:04
2  
The bath you linked has to be the shallowest bath I have ever seen. It's even called the "Shallow steel bath" in the "Low capacity baths" section of that site. I would argue that a "standard" or average bath holds around 50% more water. I also agree with dancek WRT shower flow ratings - the specifications are normally for maximum flow rate. I think the average shower pressure is much lower than the maximum. –  jozzas Jun 22 '11 at 6:31
6  
Something is wrong here... In our previous house, I'd occasionally soak my feet while showering by plugging the drain. I had a standing stall (with water-saving shower head) that was maybe 3'x3' and no more than 5" deep. I could plug the drain at the beginning of the shower and remove the plug at the end of a 10-15-minute shower. It never overflowed, and it'd have had to overflow at least 5 times over in order to be equivalent to drawing a bath. Like most people, I opened the tap fully during a shower. Also, standard bathtubs on homedepot.com are 50 gallons, or 190 liters. More for deep-soak. –  Erik Harris Sep 5 '11 at 22:59
1  
Seems like there might be a bit of a cultural bias to this question and answer. –  rob Apr 18 '12 at 2:15
show 2 more comments

This is a tough question to answer as there is going to be cultural bias at play as different countries are going to have different "standard" sized tubs and different techniques for bathing. Case and point are some of the comments in Skliwz's but also, if you look how the typical Japanese "shower" is done or even a "Navy shower" then you will note that you can get pretty extreme with the water savings. Using the "Navy shower" example with the cited 11 L (3 US gallons) then showers would come out ahead as long as you are using bucket larger than 11 L. If I take a fairly typical 5 US gallon (about 19 L) bucket then the cited argument is going to be false.

To look at things from the perspective of the United States I'll take a shower head and bath tub on the unscientific method of "cheapest possible and therefore what you will typically find in a typical apartment in the United States". This gives us a 42 US gallon tub and a 2.5 US gallon per minute shower head 1. Assuming that the average shower in the United States is eight minutes then that means the shower consume 20 US gallons of water were as the tub would be fixed at 42 US gallons on the upper end (i.e. someone climbs in to the tub after it reaches the max fill) and likely around 21 US gallons if they climb in after it reaches the halfway mark. 2

So in the end, it all depends and there are a lot of variables at play with this statement. Odds are, depending upon where you are, you could manipulate the statistics to show that any of the above are going to be the most efficient although generally speculation the bucket is likely to be the most efficient in terms of water usage if the proper bathing technique is used. 3

  1. Note that I'm bending the methodology here a bit as the cheaper shower heads were plastic and this was the cheapest metal shower head.
  2. We could get a lot more accurate with these calculations, but then you also have to account for the fact that most people can't submerge their full body in the water and are likely sitting in the tub with most of their torso outside of the water. Also, you need to account for people that "top off" the hot water in the tub if they are soaking and it starts to cool off.
  3. i.e. If someone hands you a bucket, a washcloth, and some soap and tells you to clean yourself up using what you have, you will figure out how to make it work regardless.
share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.