There is a particular fallacy I encounter often, and I don't know if it has a name already. I call it the salt in pasta water fallacy. In this post I will present the fallacy, discuss why I believe it is a fallacy, and give a concrete example of it happening.

Salt in pasta water

The archetypical example of the fallacy is the following claim: Adding salt to pasta water reduces cooking time.

The proof for this statement can be described as follows:

1. When cooking pasta, the higher the temperature of the water, the lower the cooking time
2. The temperature of the water is its boiling point
3. Adding salt to water increases its boiling point
4. (3+2) Adding salt to water increases the temperature
5. (4+1) Adding salt to water decreases the cooking time

"All of those points seem very reasonable", you may be wondering, "where is the fallacy?" Is there some sneaky chemistry phenomenon going on? 

AFAIK no, there is none. My objection goes a bit deeper.

Let's do the math

First of all, can we estimate how big the effect is? To do this, we need to know three things:

• How does the temperature affect cooking time? I found a paper^[1] from which I derive the following first-order approximation: each extra °C decreases the cooking time of 30 seconds.
• How does salt affect the temperature? I found another paper^[2] which claims that the boiling point is raised one degree for every mole of salt (i.e. for every 58g) per liter.
• How much salt does one typically add to pasta water? This is more personal, but it seems that about 5g/l is standard

So, now we simply multiply all of this and obtain... 2.6s. By adding salt to pasta water, one saves 2.6 seconds of cooking time.

Where is the fallacy again?

You may be wondering where I am going. The initial statement seemed true, I just added numbers, so what? Where is the fallacy.

The fallacy, I claim, is that 2.6s are nothing. Adding salt does not decrease cooking time. It doesn't increase it either, it just does nothing (wrt cooking time at least). This may seem weird to you, and I will try to detail it a bit more. The fallacy, I believe, lies in some play-on-word. 

Assume for example that my friend Bob and I are in front of a cooking pot, waiting for the pasta to be ready. And Bob says "adding salt will reduce cooking time". What does this sentence mean?

1. Does it only mean that adding salt will reduce cooking time?
2. Does it mean that we should add salt, because it will reduce cooking time (and we want to reduce cooking time because we are hungry/bored/something else)?

I want to argue that, in this context, it has to mean (2). And, in this context, I want to claim that Bob is wrong, such a tiny reduction in cooking time doesn't justify doing anything, or even arguing about it.

Now comes the weird part. Assume that I do the math in front of Bob, and we both agree that the math is correct and it won't have an effect greater than 3s. Bob could still claim "Ok, so adding salt does reduce cooking time, you are being stubborn". Bob is now claiming he meant (1) the whole time, the proposition adding salt reduces cooking time is true. And I'd like to claim that, no, he was using meaning (2), and just backed to meaning (1) because he was wrong.

A concrete example

This winter, in France (and, I assume everywhere else in Europe), the government wanted the whole country to save energy (this had to do with the war in Ukraine and the sudden drop in Russian gas supply). A whole strategy was devised to reduce energy consumption, one aspect of it was a set of recommendations, targeted to households, and broadcast through TV, radio, and other media. I will only list the two most iconic:

1. Lower the temperature at home to 19°C
2. Turn off the wifi during the night

(1) is a very effective idea. The government claimed that each degree would reduce the energy consumption of the whole country by 7%, which implies that each degree saves 185 TWh/year^[3]. (2) is a salt in pasta water fallacy: an average wifi router consumes 6W, which means that, if the whole country (30M households) turns off the wifi 12 hours a day, this would save, over a year, 0.8 TWh^[4]. 

But, if pushed too hard, a member of the government could always say: "even if the effect is small, it is still there, every MWh saved is a progress". To which I'd like to answer "No, you are wasting everyone's time by proposing useless solutions to a real problem".

Summary

This fallacy occurs when a claim is made (adding salt will reduce cooking time, turning off the wifi will save energy), that is both true, and negligible. The claim may convince one to do something (add salt, turn off the wifi), even though the advice is completely useless. This is a fallacy because the person making the claim can always argue that "The claim is true", in some logical sense, while the person receiving the advice is mislead to believe that is "The claim is relevant". It is difficult to fight the person making the claim, because they could always shift the debate toward the truth of the claim.

My flatmates and I lowered the temperature this winter. We do not turn off the wifi. I still put salt in the pasta water because it tastes better, and I put a lid on the pot because it saves energy/cooks faster. Or maybe it doesn't, I don't know, I never checked.

1. ^{^}

   https://doi.org/10.1002/jsfa.11138, table 4

2. ^{^}

   Boiling Point Rise Calculations in Sodium Salt Solutions | Industrial & Engineering Chemistry Research (acs.org)

3. ^{^}

   Although this probably affects only a third of the year

4. ^{^}

   On top of that, the energy from the router is not wasted, it turns into heat, thus they collectively act as electric heaters. The energy saved by turning off the routers is thus probably much smaller