Water Discounting Soap: How & Why

water dicounting

Water and lye are crucial components of cold process soap. Water is used to dissolve the sodium hydroxide lye so it can interact with the oils and begin the saponification process. As the soap cures, some of the water evaporates and makes a harder, longer-lasting bar of soap. How much water you use will depend on the calculator you use. You may also choose to water discount the recipe and use less than what is called for. If you’re unfamiliar with how the saponification process works, click here to learn more about the balance of lye and oils.

There are several reasons why you may want to water discount soap. Water discounting helps the soap release from the mold faster and results in a shorter curing and drying time, as there is less water to evaporate from the soap. Makers may also choose to discount if the recipe contains additives that naturally contain water, like fruit or vegetable purees. Using less water can reduce the chance of soda ash and glycerin rivers. In addition, it affects the temperature at which soap goes through gel phase. Water discounting has plenty of benefits.

glycerin-rivers

Water discounting is a great way to prevent the glycerin rivers shown above.

You may be thinking, “If there are so many great reasons to water discount, why don’t people do it all the time?” The trick is that water discounting a recipe can cause the soap to thicken quickly. Generally, the more a recipe is water discounted, the faster the soap thickens. This is because the lye solution is more concentrated, which speeds along the emulsification process. The water content also affects when soap goes through gel phase and how it reacts to heat. A fantastic (and beautiful!) demonstration of this is shown in The Ghost Swirl by Clara of Auntie Clara’s Handcrafted Cosmetics. In this post, Clara demonstrates wonderfully how soap is affected by water content.

Because a water discount causes the soap to accelerate faster, they can make a recipe difficult to work with. If your recipe contains a large amount of hard oils or an accelerating fragrance oil, you may want to avoid water discounts. We generally recommend water discounting for more advanced makers who are prepared to work with a faster-moving trace. If you’re looking for more information, the All About the Trace post is full of tips and photo examples of thin vs. thick trace.

thick trace

Technically, there isn't an absolutely correct amount of water to use in your soap recipe. In fact, if you plug in your recipe of soap making oils into various lye calculators, you may end up with slightly different amounts. Water is roughly 22% of the total recipe (oils + lye + water) when calculated with the Bramble Berry Lye Calculator. Other lye/soap calculators may give a slightly higher or lower amount. The amount of water in a recipe is determined by the amount of lye, not the amount of oils in your recipe.

The important part of determining how much water to use in your recipe depends on the ratio of lye to water you prefer. Remember, the lye solution is created by dissolving and diluting lye into distilled water. A common dilution rate is 30% lye and 70% water. In other words, the total makeup of the lye mixture is 1 part lye to 2.3 parts water. When the ratio of lye to water increases, the mixture is more lye concentrated. For example, a solution with 40% lye and 60% water (with a ratio of 1 part lye to 1.5 parts water) is more highly concentrated, because it contains less water in the total mixture.

lye collage

The Lye Calculator produces mixtures with a ratio of roughly 1 part lye to 2.4 parts water. This ratio will change slightly depending on the superfat percentage of your recipe. 

Some makers prefer to not use the water amount given by lye calculators at all. For example, Amanda of Lovin’ Soap Studio prefers to double the amount of lye in her recipe to get the water amount. Read more about her water calculation here. How much water you choose to use in your recipe depends on personal preference, in addition to the oils, fragrance, colorants, and additives in the recipe.

If you have decided that you’d like to water discount your soap recipe, there are a few ways to go about it. Let’s take a look at the recipe below from the Creamy Orange Cold Process Tutorial:

13.6 oz. Olive Oil - Pure(40%)
8.5 oz. Palm Oil (25%)
8.5 oz. Coconut Oil (25%)
3.4 oz. Cocoa Butter (10%)
4.8 oz. Sodium Hydroxide Lye
11.2 oz. Distilled Water
2 oz. Orange 10X Essential Oil

If you are looking at the total weight of this recipe (oils + water + lye), the water makes up 22% of the recipe. The lye to water ratio of the lye solution is roughly 1 part lye to 2.3 parts water. This is equivalent to roughly 30% lye and 70% water. Let’s do a water discount of 10%. Ninety percent of 11.2 is 10.08 (11.2 x .9 = 10.08). We can round this up to 10.1 oz. to make it easier to measure. This is the new water amount for your recipe. The amount of lye will stay the same. Remember, when you decrease the amount of lye, you are creating a lye discount which will increase the superfat of your soap. The lye and water solution will now have a ratio of 1 part lye to 2.1 parts water. Or, the mixture is now 32% lye and 67% water. This seems like a small change, but it can make a big difference.

It is possible to water discount too much. If your solution contains too much lye and not enough water, the mixture can become extremely hot and very, very dangerous. In addition, the lye may not have enough water to dissolve fully. In general, the absolute highest ratio of water to lye is 1:1. This means there is equal parts lye and water in the mixture, or 50/50. At this ratio, the lye is still able to dissolve, but will be very concentrated and somewhat difficult to work with. I do not recommend this ratio of water to lye. Some advanced makers use a ratio of 40% lye to 60% water, but this is still an extremely concentrated solution, and may be very difficult to work with.

So, when should you water discount your soap? Technically, you can water discount any batch you’d like. Just be prepared to move quickly. You may want to have a backup plan if the soap becomes too thick. If you’re adding ingredients that give the recipe additional water (like purees) that’s also a good reason to do a water discount.

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The Pumpkin Spice Swirl Soap is made with pumpkin puree, so we used a 15% water discount.

A great example of water discounting a recipe to account for water-filled additives is the Pumpkin Spice Swirl Cold Process Soap. This recipe contains 2.5 oz. of pumpkin puree, which contains water. It’s tricky to know for sure just how much of the puree is comprised of water, so it’s a bit of a guessing game. We went with a 15% water discount, which gave us a ratio of about 1 part lye to 2.1 parts water. We could have done a little bit of a steeper discount, but we wanted to make sure we had time to swirl. How much you water discount depends so much on your recipe, personal preference, and comfort level.

If you have never worked with a water discount before, we recommend starting with a 10% discount. This is a good starting point that you can increase once you get the feel for how your recipe behaves with a more lye concentrated solution. We also recommend keeping your design fairly simple, just in case. Layers are a good design option for experimenting with water discounting, because thick trace will help keep the layers separate.We rarely go above a 15% water discount - the only time we do is if we need the soap in a hurry and want to cut down on the drying time.

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Just to summarize, below are some pros and cons for water discounting your soap.

Pros of water discounting:

  • Generally, the soap unmold more quickly.
  • Reduced water in the recipe cuts down on the 4-6 week cure time.
  • Less water can prevent glycerin rivers. This is particularly helpful if your recipe contains a large amount of titanium dioxide or if you plan to insulate it. Click here to read more about what causes glycerin rivers and how to prevent them.
  • Water discounting your recipe can help prevent soda ash. Click here to read more about soda ash and how to prevent it.

Cons of water discounting:

  • Water discounting can accelerate trace, which can result in very thick soap. Click here for more information on trace.
  • If your soap accelerates, it can make some complicated soap designs like swirls difficult to execute.
  • Water discounting can make it more difficult to work with accelerating fragrance oils. Read more about working with accelerating fragrance oils here.
  • Soap with a lower water content requires higher temperatures to go through a full gel phase. If you like your soap to go through a complete gel phase, water discounting makes this a little more difficult. See a beautiful example of this in The Ghost Swirl by Auntie Clara’s Handcrafted Cosmetics.