Thought Leadership

What cost cleanliness?

By Colin Walls

As an engineer/scientist [at heart], I like things that are measurable. Being able to measure something helps me to make decisions on what I feel is a rational basis. There are many aspects of life where we rely on our perception of things. It turns out that this is a very shaky basis for decision making…

Nearly two decades ago, we were all shocked by the 9/11 atrocity. The effects – primarily on our behavior when traveling – are still felt today. The short term effect was that many people did not feel safe flying. That was their perception. Statistics say that flying is incredibly safe – much safer than driving, which many people chose to do. The result was that, in the 24 months after 9/11, more [additional] road deaths occurred in New York state and nearby than there were people killed in the planes and the towers. Relying on perception was very unhelpful and the result was tragic.

On a much more prosaic note, someone made a very off-hand comment to me about a relative staying with them for an extended period. She was complaining about the amount of time they spent in the shower. “He’s costing me a small fortune” she said. I started to wonder if this was true. Putting aside the precise definition of “small fortune”, what does it cost to take a shower? That must be measurable.

So, how do you figure out what a shower costs? Here are some factors:

  • How much water is used? That will depend on the duration of the shower and the water flow rate. I figured that the way to do this might be to take a shower in a place where it is at the end of a bath tub, leaving the plug in. Then bail out the water from the bath, measuring it as you go. A better way would be to take a sample from the shower for a fixed time and calculate the total from the duration. Obviously, an individual might shower for variable periods of time and differing pressures. Sampling, say, half a dozen showers might give a useful number.
  • The cost of the water can easily be calculated if you have a metered water supply. In many places you get to pay separately for waste water, so that must be included in the calculation.
  • The cost of the energy for heating the water is not too hard to calculate. You need the temperature of the water being used, the starting temperature of the water [i.e. cold tap temperature] and the volume, as determined above.
  • The cost of soap, shampoo etc. is hard to work out. Maybe a guess might be one tenth of the price of a bottle/bar?

That sounds about it. This number would give an idea of whether a small fortune is being spent. However, when I thought about it some more, there are other costs:

  • Laundry of towels. What does it cost to wash/dry a towel and how often is that done?
  • The price of buying a towel should be amortized across its lifetime. How many showers will it last
  • Cleaning the shower takes time and materials. Materials cost money and time should be treated as money.
  • The installation of the shower itself cost money. Again this should be amortized across how many showers it delivers in its lifetime.

I was quite surprised at how complex the cost estimate of something as simple as a shower could be. It gives me great respect for people who estimate enormous projects and shows why over-spends are so common.

BTW, you might wonder why I developed an interest in this topic. In “normal” times, I habitually get up early and go swimming – or at least immerse myself in water – every day. After that activity, I have a shower, but that is at the spa, not at home. So I rarely use [and, hence, pay for] the shower at home. One more reason to hope that some kind of normality will return …

I have thought about applying this kind of analysis to my coffee machine, but I have a feeling that I still make good cups of coffee a lot cheaper than going to Starbucks. But that is just perception …

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This article first appeared on the Siemens Digital Industries Software blog at