What is a water discount in soap making? - The Soap Coach
What is a water discount in soap making

Water discounting in soap making.

What exactly does it mean? How does it affect my soap? Is a water discount good?

I am going to keep this topic really simple. I have read too many other posts on either social media or forums where the answers are convoluted, complicated, start quoting calculations which becomes unnecessarily overwhelming.

In a nut shell, you need to use water (or some form of liquid) as part of your recipe to make soap. It has to be a sufficient quantity to fully dissolve your lye but the exact quantity is not set in stone. A good rule of thumb would be to use twice the amount of water that you have lye. So if your recipe calls for 130g of lye for example, 260g of water would be a perfectly workable recipe.

However, the quantity of water you use does have an effect on how your soap batter behaves and how quickly you can unmould,  I will expand further on that topic in just a moment.

Soap calc, which is my soap calculator of choice, automatically defaults to a water % of 38% which is way too high in my humble opinion. Your soap will take days to harden enough to unmould and you have a large amount of water that will need to evaporate during the curing process. I also find with hot process soap in particular that if you use 38% water the bars warp as they cure.

To put this is to context a batch of soap with 900g of oils and 38% water would need a whopping 342g of water.  Compare that to the 260g I have described above on a 2:1 ratio and you will see where I am coming from. Incidentally 260g of water is 29% or thereabouts. 

What happens when you use less water and is it a good thing?

There are useful benefits to using less water (and some negatives)

Cutting water content will reduce your risk of soda ash and glycerin rivers.

It will mean you can unmould your soap a little faster and it can prevent your soap from overheating once in the mould which, on occasions, will cause that annoying crack along the top.

Using a water reduction is also particularly helpful with a recipe that is high in soft oils.

Your lye solution will be more concentrated and it will begin to saponify a little faster.

Water discounting

What are the negatives of using a water reduction?

Your lye solution, being more concentrated, will initially be hotter when you mix it, not a major issue in itself but just something to be aware of.  

Because you are using less water you will need to be extra careful that your lye is fully dissolved before using it.

With a water discount it is harder to get a full gel because your soap does not heat up as much. You can get around this by soaping at a slightly higher temperature and keeping your soap warm after moulding.

Your batter will begin to thicken up faster as you are working with it meaning you have less time to create patterns and swirls.

Is there an ideal water % to use?

No,  that would be far to easy for soap making wouldn't it 😆

As is so often the case it is very much a personal preference. In my soap making workshops we always use a water % of 33%. This is a little more forgiving from a beginners perspective. It gives a reasonable amount of time to work with the batter before it begins to thicken up. It carries with it a risk of soda ash but we try to negate this with isopropyl alcohol and for me, I feel the chance to create lovely patterns and swirls is a golden opportunity to really feel happy with your first batch of handmade soap.

For soaps that I am making myself in demos etc I use around 28% water. I am happy at this level, I know I can control trace sufficiently to maintain a fluid batter and it really makes a huge difference in reducing soda ash and glycerin rivers. 

You can take the water level down even further - to 25/26% and if I was making for example a 100% olive oil soap I probably would do this.

Are there any other circumstances where it would be beneficial to reduce the water?

Yes very much so, if you are using a recipe with vegetable or fruit purees I would use a lower water % as you need to offset the water in those. How much by would depend on how much puree you are using and therefore an element of trial and error. You will also need to bear in mind other factors, ie a fruit puree will be high in sugar which will raise the temperature of your soap as it saponifies, using a water discount will help keep the temperature down but in that scenario you may not need to keep your soap warm or work at a slightly higher temperature - that however is a topic for another blog post.

What about when not to water discount too much?

There are a couple of scenarios that spring to mind here, firstly when you are making milk soaps, you may not want to use a lye solution that is too concentrated as the hotter it gets the greater the risk of your milk scorching.

The second is if you are making a fast tracing soap recipe such as 100% coconut oil. This thickens up quickly once you reach trace as it is and you most likely want to speed it up even more. I would still reduce from 38% to 33% but I probably would not drop much below that.

I hope this has been helpful. Like most things in soap making there is no right or wrong only plusses and minuses.

Yet to learn to make soap? Check out my live Zoom courses held through out the year. Watch , learn, ask questions along the way and you will be the master soap maker in your house in no time at all.

Comments (3 Responses)

07 April, 2021

The Soap Coach

Soap Calc won’t tell you if your water is too low I don’t think. I am not sure how low you could go before the lye won’t dissolve properly tbh although I am sure there is a calculation for that somewhere.

07 April, 2021


Hi there! Will Soapcalc tell you if your water is way too low or dangerous? I’m just curious I use 25% in my recipes.

05 April, 2021

Carmen Forder

Thanks for these notes, Keri. You have raised some interesting points which are very important. I will bear these points when making soap from now on.

I haven’t tried the coconut milk soap yet. I keep cutting/slicing my fingers during food prep, and I don’t like the thought of using lye when I have cuts on my hand. I am looking forward to having a go, though, perhaps before the month is out! 😊

Take care.

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