Updated: Jul 21, 2019
One of the most commonly asked questions that I see in soap making groups is “Do I really need to use distilled water in my soap?” It seems silly that we would need to spend time driving to the store, waiting in line, and then paying additional money just for water, especially when we already have all the water we could ever want in our own homes. So, what exactly is distilled water and why is it recommended for soap making?
Distilled water is water that is created through the process of distillation. Distillation is a procedure that involves the removal of contaminants found in freshwater sources, including river, lake, rain, well water, and tap water. The contaminants include inorganic materials, minerals, metals, and more. Although your tap water may be safe to drink and use for bathing purposes, it can include contaminants that are not beneficial for soap making. Water that contains these types of contaminants is often called hard water.
During the process of distillation, water is heated past its boiling point so that it changes from a liquid to a gas (steam). The steam is collected separately and then cooled to a temperature that causes it to revert back to its liquid form. After the process is complete, the contaminants that remain in the original chamber are left behind and the clean water that was collected has been distilled.
We know that water has a boiling point of 212F/100C, but the contaminants in the water have a boiling point that is higher. For example, the boiling point of calcium is 2,703°F/1,484°C and the boiling point of magnesium is 1,996°F/1,091°C. These are much higher than the boiling point of water, and they are left behind as the water boils out. Other contaminants that are removed include sodium, iron, manganese, fluoride, nitrate, lead, chlorine, and more. The process of distillation can also inactivate microorganisms such as bacteria, viruses, and protozoans.
Contaminants found in undistilled water can cause complications and unwanted reactions in our soap. These include accelerated trace, oxidation, soap scum, decreased cleansing abilities, decreased lather performance, cloudiness in liquid soap, microbial contamination and more. Contaminants increase the risk of oxidation through excess oxygen and contact with metals. This increased risk of oxidation is often visible by signs of rancidity, which include the formation of DOS or Dreaded Orange Spots, discoloration, and foul odors. Another complication of undistilled water is the formation of soap scum. Two of the most common contaminants found in hard water are calcium and magnesium. When soap and minerals like calcium and magnesium are combined, a new chemical compound is formed most commonly called soap scum. Soap scum is created when the alkali cation is replaced by either calcium or magnesium. When the sodium cation from sodium stearate is replaced by calcium found in hard water, it forms calcium stearate, a white, poorly soluble substance most often seen as a film or residue in showers. Soap scum reduces the lathering ability of soap, forms insoluble compounds, increases the risk of rancidity and more.
In liquid soap, the use of undistilled water can create a whole new plethora of complications, in addition to the increased risk of oxidation. By using undistilled water, the contaminants can react with the soap in our solution and cause problems that are visible from the very moment the water and soap are combined. It is incredibly difficult to get a clear liquid soap without the use of undistilled water, which happens to be one of the most commonly overlooked causes of cloudy soap. Additionally, contrary to popular belief, the pH of liquid soap alone is not enough to prevent the growth and reproduction of microbes. If water that is contaminated with pathogenic bacteria is used to dilute liquid soap, it has the potential to spread disease. Not all tap water can be considered clean water, and many countries do not have access to safe water.
But what about my bottled, filtered or mineral water? Bottled water companies purify the water and then add ingredients back. For example, SmartWater contains calcium chloride, magnesium chloride, and potassium bicarbonate. Nestle Pure Life includes calcium chloride, sodium bicarbonate, and magnesium sulfate. And these are just a few brands. Do these chemicals look familiar? These are some of the same chemical compounds that can form soap scum and can cause oxidation. Your at-home water filtering system may be able to filter large contaminants, but these types of filtration systems do not remove all contaminants and many contaminants remain, including metal ions like calcium and magnesium.
What happens if we don’t use distilled water in our soap? Will hard water completely ruin our soap? It’s not likely, but if you compared a bar of soap made with a high concentration of calcium and magnesium stearate to a bar of soap made with distilled water, the hard water soap would have a poorer lather performance, have fewer voluminous bubbles, may feel slimy or leave more residue, and will be more prone to oxidation. You can certainly use tap water to make your bar soap, and many soap makers do, but it should just be noted that there is a difference between soap made with and used in hard water, compared to soap made with and used in distilled water. If you have the opportunity to use distilled water, use it!
Sourcing Distilled Water
Where can you get distilled water? You can purchase distilled water locally, or you can distill your own. Distilled water can be found in almost every grocery store and is very affordable. In the U.S., most grocery stores sell a 1-gallon container of distilled water for only $0.80. If you have a water store nearby, they might have more affordable pricing, bulk sizes, and home delivery options.
You can also distill your own water using a home-distillation machine which can be purchased online, or you can distill your water through a boiling process, although these can often be more time-consuming. I want to point out that simply boiling your water in a pot is not distilling water, and this is a common misconception regularly suggested in soap making groups. From what we just learned, if we simply boiled water in a pot and didn’t collect the gaseous water separately, all we are doing is evaporating some of the water- the contaminants still remain.
UG2HP Hard vs Distilled Water Experiment
Want to try a fun experiment? This is one of my favorite experiments to do with my students. You can use this test to see if you have hard water at home . This experiment will also allow you to see the differences between hard and soft water and their effect on soap appearance, performance and lather quality.
Materials Needed: Liquid soap (not detergent, pure liquid soap), tap water, distilled water, and two clear containers with lids
1. Fill the first container halfway full with distilled water
2. Fill the second container halfway full with tap water
(If you don't have distilled water at home, you can still complete this experiment with just your tap water. If you also use an at-home filter or have bottled water, feel free to use it as a third test sample)
3. Add a dime-size amount of liquid soap (pure soap) to both containers and mix thoroughly until dissolved
4. Shake the containers vigorously. Notice the differences between the two samples, in particular, lather quality and clarity.
5. After 5 minutes, review the samples again.
From the example above, you can see that the bottle on the left that used distilled water has a large amount of big, full and voluminous lather and the water is completely clear. The bottle on the right with hard tap water is cloudy, has diminished lather, and the bubbles were very short-lived. Filtered water will have a similar appearance and performance to that of tap water. If you have very hard water, the test results will be significantly different. If your water is softer, they will not be as noticeable, but there will still be a difference. This is a great example and experiment that allows you to see for yourself the difference that hard and soft water makes on liquid soap clarity, soap performance, and the lathering abilities of soap.
Side note: If you have been formulating your recipes using soap science and creating informed recipes, but still can't seem to get a quality lathering soap, your hard water may be to blame. This experiment can help you identify this. With this information, you can then adapt your recipe and include a chelator to improve your soap's functioning.
Did you perform this experiment? Share your results with us! We would love to see them!
Do you have hard water at home? Fight hard water with a chelator like EDTA, sodium gluconate or sodium citrate. For more information about these topics, be sure to get your copy of The Ultimate Guide to Hot Process Soap by visiting our bookstore today!