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The Telegraph reported in 2008 that British historian Ruth Goodman:

stopped using soap in her washing machine and says the clothes come out just as clean. "We're all victims of 150 years of hype by the detergent industry," she says. "We don't need it."

Is it true, at least for people living in circumstances apparently similar to Goodman's, that the action of detergents in washing machines provides no benefits, and plain water would work as well?

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    This is related: skeptics.stackexchange.com/questions/5381/… – bdsl Mar 4 at 21:08
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    "Just as good" is really a relative claim. If she had a crappy machine, used lousy detergent, didn't follow recommended instructions, had hard water, etc, that could be a factor of the baseline filth generally left on her clothing, as well. I would think that Consumer Reports being able to test and rate differences between detergents would mean that detergents don't just do nothing.... hmmm, I have the beginning of an answer here.... – PoloHoleSet Mar 4 at 22:14
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    @PoloHoleSet And you should go ahead with it. But do you have something that goes directly to such a comparison and does not rely on (really plain) logic. The claim looks so much like bogus, I'd really like to see it repeated at one more time anywhere. – LangLangC Mar 4 at 22:22
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    Soap or detergent? They are two different things. – Daniel R Hicks Mar 4 at 23:39
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    As a single data point, I now have a couple shirts that smell kind of damp and are more wrinkled than usual. I'm sticking with detergent. – Giter Mar 5 at 2:45
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It seems like there are two parts to this question, and, perhaps, OP will tighten up the language a bit.

Do we need to use detergent in washing machines?

Depends on what you want when you wash your clothing, I suppose. It's possible, that for some people, the amount of dirt and soil removal from just rinsing is adequate. That's a matter of personal preference.

But if you are asking -

Does detergent make any difference vs plain water?

That's a different question. Generally speaking, yes, there is a difference. But what about Ruth Goodman's claim? It could still be true, and the answer that detergents do/can make a significant difference could also be true. How?

NOT ALL WASHING CONDITIONS ARE THE SAME

We really don't know what conditions Ms Goodman used for her washing all of those years. Detergent, water conditions and level soil being equal, some machines do a better job of washing than others.

A look at performance We've reviewed dozens of washing machines. While we still have a long way to go before we've tested all of the models on the market, top-load washers have earned our best (and worst) stain removal performance scores so far.

In contrast, the front-load washers we've reviewed tend to fall somewhere in the middle performance-wise, with a few outliers on either side.

CNET Washing Machine Buying Guide

Equal machines and soil level, having hard water will inhibit the ability to clean clothes.

Soap and detergent simply don’t work as well in hard water. Those dissolved minerals hamper the effectiveness of many cleaning products.

That’s because minerals like calcium and magnesium prevent water from mixing with detergent to form a solution. As a result, soap scum gets left behind. The same white, chalky substance in your sink and shower gets on your laundry. Sometimes, the stuff that sticks to the fabric is referred to as “detergent curd,” which sounds even more disgusting.

The result is dingy looking clothes that don’t feel completely clean after they come out of your dryer. The residue on your clothes will even attract and hold more dirt as you wear them.

WaterRight Group Blog: Is Hard Water Ruining Your Laundry?

NOT ALL DETERGENTS ARE THE SAME

All other factors being equal, some detergents to a very good job (some perform better or worse in hard-water or particular water temperature situations, as well), and other ones are poor quality, just like with any other product.

Consumer Reports (CR, for short) is known for objective product testing. They test many kinds of laundry detergent under many different conditions, and there are definite differences between the detergents. By definition, if detergents really did nothing, you wouldn't see a difference. However, as a control group for comparisons, CR would also run a plain water wash for their tests, so we don't really have to speculate about that. The worst of the detergents performed barely better than plain water. The best ones did much better.

Consumer Reports recently tested over 50 different detergents, including a new one from homemaker Martha Stewart. They set out to find which are worth your money, and which ones are like putting money down the drain.

In the study, all detergents faced the same challenge: washing in both top-loading and high-efficiency washing machines. Material was also washed using just plain water in order to see what difference, if any, the detergents made.

Martha Stewart's detergent, for example, claims it "removes tough stains." Consumer Reports used swatches riddled with some "tough stains" (rings around the collar of a shirt, wine, grass and blood, just to name a few) to see if any differences could be observed.

After washing the swatches, testers used a special device to precisely measure how much of the stain had been removed. So how did the decorating queen's detergent do?

In conventional top-loaders, there was barely a difference between the swatches washed in Stewart's detergent, and those washed in plain water. The results of her detergent in the high-efficiency machines fared better, but only slightly.

Wave3 News: Could plain water clean as well as high-priced detergents?

(Note: Consumer Reports' testing results are behind their pay wall, otherwise I'd directly cite their results and commentary for you).

So, according to objective tests, decent-quality detergents did make a significant difference in cleaning laundry vs. plain water. They do use measuring equipment to discern between results that are close together, but getting a stain completely out vs. mostly out vs the stain pretty much being there would be a significant difference to even a fairly casual observer.

CR’s testers wash fabric swatches that are saturated with blood, chocolate, red wine, dirt, grass, tea, and body oil. These are tough stains to remove, and we use them to challenge the detergents so that we can detect real differences among them. Using cool water, we wash the swatches in three identical washers with each detergent. We then allow the swatches to air-dry. (A dryer is out of the question because the heat can alter the stains.)

Testers use a colorimeter, a device that measures color intensity, to see how much of the stain remains on each dry swatch, compared with stained swatches that have been laundered using only water.

Consumer Reports: Tide Beats Persil in CR's Laundry Detergent Tests (behind paywall and not viewable without an account)

However, the worst ones didn't. And it wasn't necessarily "cheap = low-quality," as Stewart's product carried a premium price tag.

If Ms Gordon had any combination of inferior machine, poor water conditions, not following recommendations for her detergent, or inferior detergent quality, it is entirely possible that she saw no appreciable difference in her detergent vs plain water, while it also being true that detergents can make a big difference, as well.

As product manufacturers like to remind us, "Results May Vary."

Addendum: Here's an article, directly from CR about which machines and detergents people should avoid, that they posted, available for free to the public, as a service. It doesn't add a ton more detail, but I figured, straight from the horse's mouth instead of second-hand adds a bit more backing to my answer:

Laundry Detergents

With laundry detergents, you can waste money a couple of ways. Detergents that don’t clean well might require you to redo a load. And if you don’t measure the detergent, you might end up using more than you need.

These detergents were no match for common stains such as body oil, dirt, and grass. You’ll find much better detergents in our laundry detergent ratings.

Among liquid detergents, Xtra ScentSations and Trader Joe’s Liquid Laundry HE detergent clean only slightly better than plain water. You can also skip Xtra Plus OxiClean and Sun Triple Clean.

Consumer Reports: Laundry Products That Waste Loads Of Money

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    Oh wow. These testers are surprisingly crazy… My anecdotal evidence (forgot to add detergent a few times) said that these "difficult stains" go away with pretty much any detergent I ever bought and stay put if no soap is in the load. But I read that "barely better" as: "better than water alone in every case, still" (what's your "significant")? I don't see how hot they run their pure water tests (as fatty dirt gets dissolved in hot water OKish). Add this and re-run my own tests on purpose. – LangLangC Mar 4 at 22:49
  • @LangLangC - They take swatches of cloth, and stain them with mud, blood, chocolate, coffee, tomato sauce, etc. Run them through the different washes with a normal load of laundry, then take the swatches, compare them to the other swatches, and the original fabric swatches that were never stained, and base their assessments on how they compare to the original vs each other, visually. I'm adding another reference directly from CR, FYI. – PoloHoleSet Mar 4 at 22:52
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    The way the emphasis is set at this point, a hasty read would give the impression that "detergents are only slightly better than plain water", while I understand that this is only true for a select few, with many much better detergents available. Perhaps have a second look at how you used the boldface? – DevSolar Mar 5 at 12:50
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    @DevSolar - the emphasis was merely to show that they used plain water as a control group. That particular passage was specifically about which ones failed the test, so I can see why that impression is there. Changed the bolding to include less, and then added similar bolding to a previous passage from CR talking about how they test. – PoloHoleSet Mar 5 at 15:29
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    With regard water hardness mentioned in the answer Buckinghamshire were Ruth Goodmans home is has what is classed in the UK as very hard water over 300mg of CaCo3/l of water. – Sarriesfan Mar 8 at 3:44

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