The math of faucet-fiddling to get a constantly warm shower

Charles Betz says:
Christina Matzke at the University of Bonn in Germany and Damien Challet of the Institute for Scientific Interchange in Turin, Italy, used a mathematical model to show that shower temperature becomes increasingly sensitive to small changes in hot-water flow as the number of users increases. Thus in a youth hostel, for example, the showers often fluctuate between scalding hot and ice cold during heavy use.


  1. You also have to count in gravitational effects, if the flow is low enough. I was working in Chinhae Korea a few years back & thge water pressure was horrible, no mater what time you showered. When some else showered it got to be ridiculously bad, such a low flow I, not know for patience & tolerance, was greatly amused by how little water could actually flow out. The problem was worse when the shower in the adjoining room was used. I dropped the hand held unit at one point while Dave was using said shower & discovered that I got almost 100% flow. I then took all my showers sitting down, & never said a thing about my discovery.

  2. I reckon that faucet fiddling wastes more water than wasteful shower heads and that most water saving heads result in more fiddling. Most people here in Australia have two taps and fiddle merrily while thinking they are saving water with their piddling shower heads.

    I live in a multi storey block with communal gravity fed hot water. It was a nightmare until I put regulators (350 kPa) onto the hot and cold supplies, a good mixer tap and a quality shower head. Now I don’t change the position of the tap from one day to the next.

    Hydraulics and thermodynamics are the only subjects I got over 90% for.


  3. Russian cosmonauts were actually trained using this. In cosmonaut training, it was discovered that the most successful crews were the ones that were best able to shower together.

    No, not like that.

    The old Russian plumbing wasn’t particularly good, and as one team member changed the temperature of their water, the others would freeze or get scalded. The teams that negotiated this best — often without speaking — were the most likely to succeed in more complex tasks together.

    As a result, they engineered an electronic equivalent that had them all balance individual needles against a shared circuit. Those teams that passed this test quickly were kept together.

  4. Am I the only one who lives in a house where flushing the toilet does not change the temperature of the shower?

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