Classic Bells > Soapy stuff > Water in soap

Full water and other drippy myths

Soaping, like many crafts and professions, has its own lingo and traditions. Have you heard that beginners should only make "full water" soap and a "water discount" should only be used by the experts? Have you wondered what "water as % of oils" really means?

All three phrases relate to the amount of water used when making soap, but they are concepts that interfere with the goal of consistently and reliably making good soap. I want to explore these three drippy myths and suggest better ways to choose the amount of water for better soaping results.


Brief definitions

"Water as % of oils" is a way to calculate the amount of water in a recipe based on the total weight of the fats.

"Full water" is the idea that there is an ideal water content for all soap recipes. Beginners are often discouraged from using anything other than "full water."

"Water discount" is the term used for a recipe that uses less water than the "full water" amount.


Water as % of Oils

"Water as % of oils" is probably the worst troublemaker of the three. This is a method of calculating the amount of water based on the weight of fats in the recipe.

Most soap recipe calculators are set to a default of "38% water as % of oils." This means a soap recipe will have 38 grams (or 38 ounces) of water for every 100 grams (or 100 ounces) of fats.

The problem with using "water as % of oils" is that the amount of water in proportion to the fats is not particularly important. What is more important to the chemistry of saponification is the amount of water in proportion to the alkali (NaOH or KOH).

Water modifies how fast the alkali can attack the fat molecules.

If you want to slow the rate of saponification, use more water in proportion to the alkali. This is helpful for soap that has a lot of coconut, palm kernel, or babassu oil. Soap with these fats is notorious for overheating and cracking and sometimes even overflowing the mold like lava from a volcano.

If you want to speed up the rate of saponification, use less water. This is helpful for soap that has a lot of olive oil and similar liquid oils. This type of soap can take forever to come to trace, the soap sometimes separates in the mold, and it can take ages to harden up before the soap can be removed from the mold.

Unfortunately, the math involved with the "water as % of oils" setting does exactly the opposite -- it calls for more water to be used with recipes that need less and vice versa. The "water as % of oils" setting makes it difficult to create reliable, trustworthy soap recipes.


See the differences for yourself

Open your favorite soap recipe calculator. And if you have not yet learned to use a soap calculator, now is the time to start. Of all the online calculators available, I recommend if you are fluent in English. It is a full featured calc that is easy to use.

Set up two simple soap recipes with just water, NaOH, and fat. One will use 100 grams (or ounces) of 100% coconut oil. The other one will use 100 grams (or ounces) of 100% olive oil. Use the default setting of "38% water as % of oils" for both. Leave the superfat at the default -- usually 5%.

Look for the total water weight in each recipe. You will see the two recipes call for the exact same grams (or ounces) of water -- it should be 38 grams (or ounces) for both.

Look for the "water:lye ratio" for both recipes. Compare these two numbers. Are they the same? If not, which recipe has the larger water:lye ratio?

As the number for the "water:lye ratio" gets bigger, that means there are more grams of water in the recipe for every gram of NaOH.

A water:lye ratio of 2 means 2 grams (or ounces) of water for every 1 gram (or 1 ounce) of NaOH.

A water:lye ratio of 3 means more water -- 3 grams (or ounces) of water for every 1 gram (or 1 ounce) of NaOH.

Which recipe has more water in proportion to the alkali (NaOH)? (Hint: It is the recipe with the higher water:lye ratio.)

Is this recipe the one that would benefit from more water to slow down saponification? (Hint: No, it's not!)

In summary, calculating the amount of water based on the weight of fats makes it more likely you will have problems with your soap making. Using "water as % of oils" makes no sense if you want to have consistent, reliable soap recipes.

Your soaping will be more predictable and consistent if you calculate the amount of water based on the weight of alkali (NaOH or KOH).


Calculating Water Based on the amount of Alkali

Before I go on to "full water" and "water discount," I want to explain more about how to calculate the water based on the alkali.

There are two common ways to calculate water based on alkali, whether you are using NaOH, KOH, or both. One is "lye concentration" and the other is "water:lye ratio."

The numbers for lye concentration and water:lye ratio may look different, but they mean the same thing -- you can see for yourself in the table (below). Pick the one that makes the most sense to you and stick with it.

Many soapers prefer water:lye ratio because it is more intuitive to non-chemist types. Higher water:lye ratio => More water

Because I once worked as lab technician in a chemistry lab, lye concentration makes the most sense to me, because that's how chemists think of these things. Higher lye concentration => Less water

Water:lye ratio and Lye concentration are equivalent to each other. They are NOT mathematically equivalent to "water as % of oils."

If you are new to making soap, you might want to experiment a bit to see what lye concentration settings (or water:lye ratios) work best for you. Keep in mind that small changes in the water will make definite differences in your soap, so don't go crazy.

Here's how you can learn about this --

Using your favorite blend of soaping fats, calculate a recipe using 28% lye concentration (2.57 water:lye ratio), and make a batch of soap. See how the process goes and how the soap turns out.

Make a second identical batch except use 30% lye concentration (2.33 water:lye).

Make a third batch using 33% lye concentration (2.03 water:lye).

Evaluate the soap from the three batches. Some questions you might want to answer include --

Which recipe behaved best when you made the soap?
Did one recipe come to trace a lot faster or slower than the others?
Did the molded soap stay overly soft or was it firm fairly quickly?
Is there a difference in the appearance of the soap from the various batches?

The table below links lye concentration and water:lye ratio. I also have some suggestions for how to choose a useful lye concentration (or water:lye ratio.) I am not the last word about what works best for every soaper, so do not take my recommendations as the last word on this matter!

As you gain more experience, you will learn about other issues that can affect your choice of lye concentration, and you will eventually develop your own preferences. Other issues that may affect your choice of lye concentration include --

Food ingredients that cause soap to heat up -- Sugars (table sugar, honey, maple syrup, etc.), beer, food purees, etc.

Chemical accelerants -- Eugenol, a chemical found in clove essential oil, and some fragrances (many florals in particular)

Design plans -- Complicated swirls needing more working time versus simple swirls or uncolored soap that is faster to make

Temperature of ingredients -- Warmer ingredients tend to accelerate saponification

Intensity of mixing -- Stick blending or vigorous hand whisking tend to accelerate trace and saponification. Hand stirring with a spoon or spatula slows things down.


Lye concentration versus Water:lye ratio and suggestions for use

Lye Conc.,
Suggested usage
25 3.00 The most water in proportion to alkali that is typically used for soap.
Good for making liquid soap paste, shave soap, or hot process (HP) bar soap. Not recommended for cold process (CP) soap. CP soap with this much water may not form a stable emulsion and may separate in the mold. It is very likely to be far too soft for days after saponifying.
26 2.85
27 2.70
28 2.57 Lowest lye concentration I recommend for cold process (CP) bar soap.
Pros: Good for recipes high in coconut oil that can overheat and crack. May work better for complicated swirls, depending on the soaper and the recipe. Cons: Soap is more likely to gel during saponification, which you may or may not want. Soap is more likely to show streaking and mottling (aka glycerin rivers). Higher chance of emulsification failure and separation in the mold. Soap may take several days to firm up enough to be removed from the mold.
29 2.45  
30 2.33  
31 2.23
32 2.13
33 2.03 Good all-around choice for most CP recipes and many CP soap makers. Pros: Chance of gelling and "glycerin rivers" is reduced but may sometimes happen. Soap gets firmer in the mold faster. Cons: Soap may trace somewhat faster than with more water, but this is not a hard-and-fast result. The time to trace also depends on the fats and your soaping methods.
34 1.94  
35 1.86  
36 1.78
37 1.70
38 1.63
39 1.56
40 1.50 Good choice for 100% olive oil soap and other slow saponifying recipes. Pros: Chance of gelling and "glycerin rivers" is very low. Other pros and cons are same as for 33% lye concentration (2.03 water:lye ratio).
41 1.44  
42 1.38
43 1.33
44 1.27
45 1.22
46 1.17
47 1.13
48 1.08
49 1.04
50 1.00 The lowest amount of water in proportion to alkali that can be used. Any soap recipe can be made with a 50% lye concentration, but most soapers prefer to use more water. This is the most NaOH or KOH that will dissolve in water at room temperature.


Full Water

Many soapers seem to assume there is some ideal water content for making cold process (CP) soap, and this ideal water content is called "full water."

A general definition of "full water" during the time I have been soaping is the water calculated by using "38% water as % of oils." All of the soap recipe calculators I have looked at and many books, tutorials, videos, and online forums use this "38% water as % of oils" as the default. I would say this definition of "full water" is what is commonly accepted by many soapers.

If "38% water as % of oils" is used to calculate the water for a balanced blend of coconut oil, olive oil, and either palm or lard, the lye concentration is about 28% (2.57 water:lye ratio). If you did the exercise I suggested earlier, however, you will know the "full water" lye concentration varies a lot when the "water as % of oils" setting is used, ranging from 25% for a 100% olive oil soap (more water) to 31% for a 100% coconut oil soap (less water).

When soapers ask for help at the Soap Making Forum, their most common complaints include the soap being too soft for days after saponification, separating in the mold, weeping liquid, showing unsightly "glycerin rivers", overheating and cracking, and so on. Many are using "38% water as % of oils" to calculate their recipes, and this is one big reason why they have these problems. These soapers would have fewer troubles if they would pick a lye concentration or water:lye ratio appropriate for their recipe and calculate the the water content based on the alkali weight.

Kevin Dunn, author of "Scientific Soapmaking," surveyed recipes in soap making books published from the 1970s through the 2000s. He found lye concentrations used by these authors ranging from 25% to 37% (water:lye ratios from 3 to 1.16). (Scientific Soapmaking, 2010 ed, pg 293-294) These authors are clearly not limiting themselves to some "full water" ideal. I suspect many of these authors have chosen a lye concentration that best suits the recipe.

There is no one best water content for all soap recipes and all soapers all of the time. The "full water" limit of 28% lye concentration (2.57 water:lye ratio) is more water than the average soap recipe actually needs.


Isn't concentrated lye more dangerous?

The risks of handling any lye solution over a 10% concentration are pretty much the same. Injury will occur within seconds at these concentrations, so if you are splashed with lye at 10% concentration or higher, you have only a brief time to react.

The precautions for working with lye are the same regardless of concentration -- you will use the same method of mixing water and alkali to make the lye solution; the same kinds of eye, respiratory, and hand protection; and the same first aid treatment.

If you have been limiting yourself to "full water" soaping due to fear of handling lye at higher concentrations, please let go of your fears.

A "full water" lye solution at 28% concentration is no safer to handle than a more concentrated lye solution.


Water Discount

The concept of a "water discount" is the practice of using less water to make soap than the "full water" amount. Since there is no clear and consistent definition of "full water," then "water discount" is another concept that has no clear, consistent meaning. The amount of water in a soap recipe should be based on practical, understandable reasons, not based on unclear concepts such as these.


In summary

If you start using lye concentration or water:lye ratio and ignore the myths of "water as % of oils" and "full water" and "water discount", you will learn that tweaking the water content a little higher or a little lower is just a normal adjustment to make, not something to be scared of.

Find the range of lye concentrations (or water:lye ratios) that works best for your personal soaping style and the kinds of soap you make. Enjoy your soaping!