Does water really matter?

Better Soaping through Kitchen Chemistry: Does Water Really Matter?

INTRO

I did a little kitchen chemistry today and wanted to share the results with you. Many people debate what kind of water to use for making soap.

I have always used distilled water when I make bar soap (NaOH) and liquid soap (KOH), but many folks use tap water for both. So if tap water works okay for many people, then why do others stick to distilled? As part of my curiosity about the science of all things soapy, here are the results of my latest kitchen chemistry experiments:

What is "hard water scum" and how can it be prevented?

Drinking water as it comes directly from a water source (well, spring, river, or lake) is usually "hard" in that it contains a variety of dissolved minerals. Dissolved magnesium and calcium minerals in this water -- the most common hard water minerals -- react with soap to form an insoluble, unpleasant paste or scum. When particles of soap scum form, they turn the water milky white and quickly stick to any solid surface. Clothes turn grey and stiff, the bathtub or shower becomes dirty and rough, and skin feels irritated and sticky.

One of the ways that hard water scum can be prevented is by "softening" the water before it is used. Some cities treat drinking water to partly soften it, but home water softeners are often used. Home softeners typically replace the hard water minerals with sodium from table salt (sodium chloride, NaCl), but it is difficult to remove all of the undesirable minerals with any water softening system.

Another way to prevent soap scum from forming is to include additives in soap that react even quicker with hard water minerals than soap can react. Sodium citrate and Tetrasodium Ethylenediaminetetraacetic Acid (Tetrasodium EDTA or EDTA for short) are two chemicals that chelate (react with) hard water minerals to reduce soap scum. The chelated minerals remain dissolved in water rather than create sticky scum. The minerals flow down the drain rather than stick to clothes and skin.

What types of water can be used for soaping?

Tap water, filtered tap water, and bottled "spring" or "drinking" water are potable (safe to drink) water. These types of water come directly from a spring, well, lake, or river with varying levels of treatment. Tap, filtered, and bottled water all contain minerals that either come naturally from the water source or are added after purification to improve the taste.

Most or all of the minerals in water can be removed by distillation, reverse osmosis (RO) treatment, and deionization. Water that has been treated with these processes tastes "flat" because the mineral levels are so low. This water is valuable for chemical processes where the minerals may cause undesirable chemical reactions. Distillation is the gold standard, followed closely by reverse osmosis. Deionization systems, unless they are laboratory quality and well maintained, are not considered quite as effective as RO and distillation.

Rain water is essentially distilled water, although it can contain dust, dissolved acids, and bacteria collected in its travels through the atmosphere. Water collected from dehumidifiers is also essentially distilled, but it too can contain dust, bacteria, etc. unless the collection system is kept scrupulously clean.

...to be continued...

PART 1: Does soap scum form in hard, soft, and distilled water?

PART 1: Method

I did a series of tests today to show the effect of different types of water -- hard, soft, and distilled -- on the performance of a lye soap. The soap I used is a diluted liquid (KOH) soap I made following Irish Lass' recipe (see note). Bar (NaOH) soap reacts chemically with hard water minerals exactly the same as liquid soap does, so my results apply to both kinds of lye soap.

Note: Irish Lass' liquid soap making tutorial and recipe are here: http://www.soapmakingforum.com/showpost.php?p=428988 Look for Posts 8 and 9. I also recommend Susie's liquid soap recipe and tutorial: http://www.soapmakingforum.com/showthread.php?t=49852

The tap water I used for this test was from my home water system in rural northeastern Iowa. We have moderately hard well water that we treat with a home water softener. I collected a sample of hard water upstream of the softener and a second sample of softened water for this test. I also used distilled water purchased from my local grocery store.

I measured out 100 g of water into several clean 1/2 pint (250 mL) glass canning jars. I added 1 gram of diluted liquid soap (LS) to each jar and stirred briefly with a clean bamboo chop stick. These were the mixtures I tested:

Jar 1. 100 g hard water + 1 g LS
Jar 2. 100 g soft water + 1 g LS
Jar 3. 100 g distilled water + 2 g sweet almond oil + 1 g LS
Jar 4. 100 g distilled water + 1 g LS

After allowing the solutions to sit for a few minutes, I photographed them against a contrasting background. (I tried a striped white towel, but found a plain red gave better results.)

PART 1: Results

After the liquid soap was stirred into each sample, I evaluated the appearance. The hard water sample (Jar 1) became opaque white within a few seconds after I stirred in the LS. The resulting solution formed very little suds and the bubbles dissipated quickly. The soft water sample (Jar 2) turned cloudy in about the same time. The mixture did form stable suds, but not as freely as Jar 4. The distilled water sample (Jar 4) remained clear and the soap mixture lathered freely.

Jar 3 is a little unusual in that I added about 2 g of sweet almond oil to the LS and distilled water in Jar 3. I did this to simulate the dilution test that liquid soapers can use to check whether a liquid soap is fully saponified. If there are unsaponified fats left in the soap, the sample will appear cloudy (Jar 3). If the soap is properly saponified, the sample should be clear.

In Jar 3, the liquid soap emulsified the oil into tiny droplets that were just barely visible to the naked eye. The resulting mixture of oil, soap, and water was slightly cloudy, somewhat similar to Jar 2. If a soap paste is tested with tap water (Jar 2), it would be easy to think the soap still needs to be cooked. But do the same test with distilled water (Jar 4), and it is obvious the soap is perfectly fine.

PART 1: Conclusions

Hard water is tough on soap! Even softened tap water reacts with soap to cut lather and form soap scum. The reaction is almost instantaneous, which is why hard water scum sticks to the skin so quickly and easily when bathing.

When making, testing, and diluting liquid soap, even softened water can create a cloudy product that doesn't lather well. If accurate test results, crystal clear soap, and maxiumum lather are the goals, it is vital to use distilled water or its equivalent when making, testing, and diluting liquid soap.

*** to be continued ***

PART 2: Does a chelator such as EDTA effectively reduce soap scum in hard and softened water?

PART 2: Method

I reserved Jar 1 (hard water + LS) and Jar 2 (soft water + LS) and set Jars 3 and 4 aside. I made up two more mixtures of water and LS that were duplicates of Jars 1 and 2:

Jar 1a. 100 g hard water + 1 g LS
Jar 1b. 100 g hard water + 1 g LS
Jar 2a. 100 g soft water + 1 g LS
Jar 2b. 100 g soft water + 1 g LS

I made a 39% solution of Tetrasodium EDTA in distilled water by dissolving 39 g EDTA in enough distilled water to make 100 g of solution. For more information about making and using Tetrasodium EDTA solution in soap, see Irish Lass' post: http://www.soapmakingforum.com/showpost.php?p=432635&postcount=19

I added 0.5 g of the EDTA solution (0.20 g pure EDTA) to Jars 1b and 2b and stirred well with a chopstick. After 2-3 minutes, the soap mixture in these jars began to clear. I added another 0.7 g of EDTA solution (another 0.27 g pure EDTA) to the same jars. After another few minutes, Jar 2b (soft water) was almost clear and Jar 2a (hard water) was just slightly hazy. After 30 minutes, the soap mixtures in both jars were as clear to the naked eye as Jar 4 (distilled -- see my previous post for the Jar 4 pic).

PART 2: Results and Conclusions

EDTA is dramatically effective in breaking down soap scum. In these tests, the soap scum had already formed, so it took some time for the EDTA to break it down. In actual use, EDTA can react directly with the hard water minerals and prevent the scum from even forming.

EDTA is not a "crunchy" ingredient, so soapers looking for "natural" recipes may not care to use it. Sodium citrate is an alternative to EDTA that may be effective at preventing soap scum. I did not have any sodium citrate handy or I would have tested it.

There is another important benefit of using EDTA or sodium citrate that comes from the ability of these chemicals to chelate (chemically react with) minerals. Soap that contains either of these additives is less likely to become rancid or develop DOS (dreaded orange spots, a sign of rancidity).

*** the end! ***

Thank-you DeeAnna for all your had work...this is very interesting and valuable information. How lucky our forum is to have a resident chemist that loves soap

OH MY GOODNESS!!! Thank you so much for posting this experiment, DeeAnna! I've read may articles and threads about the opinions on the type of water used. I've always stuck with distilled because my thinking is adding less unknown minerals will result in better soap (meaning less unknown ingredients at the end). Soap scum after the fact has always been a head scratcher for me. I've been on the fence about additives to help cut down or prevent the problem. As always, I enjoy reading and seeing the results of your well thought out, easy to understand, chemistry experiments.

I love your experiment, DeeAnna!!! <3<3<3<3

How wonderful, thank you! I use distilled or fresh fallen snow exclusively here.

Ditto what everyone else said! Great information.

My jaw dropped seeing jar number one. I was not expecting the cloudiness to be so drastic. The EDTA is remarkable in its effectiveness. I use sodium citrate so was very interested to see these results. I had used distilled water for some time in making the soap and then changed to softened tap water. I think I'll go back to distilled, even while I use the sodium citrate.

I remember traveling all over when I was in my 20s and the horrible soap scum that we got in our hair. SPent hours on our trains rides trying to pick it out of each others tresses because it was impossible to comb through, until we got someplace with better water. Seeing that white jar brings it home.

I'm a believer.
Or to save money on soap-making, maybe I'll still use tap and just re-brand mine as "Hard Water Soap." There's a niche market for everything.

The EDTA surprised me too. A dramatic change! If I had had some sodium citrate easy to hand, I would have tried it too. I would have had to make it from lye and citric acid and I just didn't feel like hauling the lye, safety goggles and gloves out for a few drops of citrate solution.

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Wow! Wonderful!!! As always, thank you so much for sharing!

Fantastic explanation. Thank you

Wow, so much valuable info there......thank you!!! I have extremely hard water, and because of what I'd read early on in my soapmaking days, I've always used distilled water. I'm glad to know that the extra expense has been worth it.

Thanks so much for doing this DeeAnna, it's really helpful.

DeeAnna amazing experiment! I'm curious what is your take is on filtered rain water? I myself have only used distilled water and other non water liquids but I have heard of others filtering rain water for their soaping.

Mish -- My take is "it depends." Rainwater can contain any contaminant that is present in the atmosphere -- soot, dirt, air pollution, "acid rain", etc. Rainwater should be filtered or allowed to sit quietly to settle out the particulates, but that won't do anything about any dissolved contaminants. If a person lives in a rural area, rainwater is probably not going to be highly contaminated with pollutants. For those living in a heavily populated region, especially if there is a lot of air pollution, then rainwater might be more contaminated than one might want.

This is a super helpful post/thread. CP newbie, so please forgive any grating mistakes. Since switching to cp, I have been getting HUGE amounts of soap scum in the shower. I thought it was the amount of oil in the cp (superfatted at 7.5), and was thinking of cutting back. It is a relief to know that I can still have lots of moisturizing!

I spent a couple of hours looking for the answer to this question for DeeAnna and Irish Lass (to whom I am very grateful for that great post demystifying the math behind EDTA solutions, critical for a math imbecile like me), do you offset the amount of water you would normally use in your lye water mix to account for what you are adding to mix the EDTA powder?



Ie; based on the example below, I need to add 10.24g of 39% EDTA/water solution for 800g of total batch weight. Normally I would add 6 oz of water to lye to make my lye water mix. Do I subtract the 10.24 g - @ .35 oz - from my normal water amount to compensate for the water in the EDTA solution, or is this small amount of added water not that big of a deal? If not, ie, I do not offset the water in the EDTA solution, will the only drawback be the soap taking a bit longer to cure (worth it, given the soap scum issue)?


Ex: I want to mix up 12 oz of EDTA solution at a .39% EDTA composition rate, and add the appropriate amount of that solution to my soap at a .5% rate, like Irish Lass. So, if I'm doing the math right it goes like this:



Step 1: Creating a "master batch" EDTA solution of approx. 12 oz (size of my squeeze bottle J):
12 oz x .39 = 4.68 oz. Jiggling the numbers at Roxanne's site, if I add 4.7 oz of EDTA powder to 7.35 oz of water, it comes out to 12.05 oz of solution at a 39.004% EDTA composition rate.



Step 2: Figuring out how much of the "master batch" EDTA solution I need for this particular batch:
Total batch weight of 800g x .5 = 4g, which is how much EDTA powder I need; 4g x 2.56 = 10.24g, the amount of the "master batch" EDTA solution I need to add to my batter.


I hope this makes sense. My poor non-mathy brain is whirling.


Thanks in advance for any advice, you guys.
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"...Do I subtract the 10.24 g - @ .35 oz - from my normal water amount to compensate for the water in the EDTA solution..."

Short answer .... I confess I don't. But if I did, I would want to subtract just the water content in the EDTA solution from the overall water, so:
10.24 g EDTA solution X (1 - 0.39) = 6.25 g water in EDTA solution

At 6 oz total water (168 g), the 6.25 g of water in the EDTA solution is 6.25 / 168 X 100 = 3.7% of the total water
Is that a big issue? Might be, depending on the soaper and the soap. If you use "full water" (28% lye solution) I could see why you might want to compensate for the water in the EDTA. I usually soap with 31% to 33% lye solution, so a bit more water is not going to put my soap at risk for separation in the mold or unusually slow saponification.

And your math for "step 1" and "step 2" is correct. Well done. Bravo!

Thank you, DeeAnna! You are always so helpful. It is nice to know that there is whizzy match brain to balance out the fizzy ones amongst us. I hadn't even thought of just taking out the water amount in EDTA mix, I would have subtracted the whole thing. I can't wait to get my EDTA and have a non-scummy shower! Thanks again.