Water in Cosmetic DIYs

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Water

Aqueous Phase Standards & The “Water to 100” Logic

In my formulation studies, water is the most voluminous and technically volatile component. Because water supports microbial life, its purity and the logic behind its calculation are the primary safeguards for a stable product.

1. The Purity Hierarchy: Beyond the Tap

The choice of water is not negotiable. Standard tap water contains minerals (electrolytes) and metal ions that can destabilize emulsions and deactivate preservatives.

  • Demineralized Water: Free of minerals that interfere with electrolyte-sensitive ingredients (like Carbomers or specific emulsifiers).

  • Microbiologically Pure Water: Required to ensure we aren’t introducing bacteria or fungal spores into the batch.

  • The “Boil and Hold” Protocol: If commercially distilled, sterile water is unavailable, I utilize a high-heat mitigation strategy. I boil demineralized water for at least 20 minutes to reduce the bio-burden. This does not guarantee 100% sterility, but it significantly increases the efficacy of the final preserving system.

2. The “Heat and Hold” Method

When executing heated emulsions, I often utilize the Heat and Hold technique. This involves maintaining both Phase A (Aqueous) and Phase B (Lipid) at 70°C–75°C for 20 minutes.

  • Objective: To ensure all high-melting-point waxes are fully integrated and to provide a secondary thermal “kill step” for potential pathogens in the water phase.

3. The Mathematical Protocol: “Water to 100”

In professional formulation, we work exclusively in Percentages (%). This ensures that the concentration of active ingredients and preservatives remains constant, regardless of the batch size or substitutions.

Why we calculate water last:

By listing water as “Water to 100,” we treat it as a flexible solvent. If I decide to increase an active ingredient from 1% to 2%, I do not reduce my preservative; I simply reduce the water. This maintains the integrity of the chemical ratios.

Example Calculation: If a formula requires:

  • Gelling Agent: 1.5%

  • Preservative: 0.5%

  • Actives: 3.0%

The math follows:

If I substitute a gelling agent that requires 3.5% for the same viscosity, the math updates automatically:

Result: The preservative remains at exactly 0.5% of the total mass, ensuring the product remains safe.

Researcher Summary

“Water to 100” is the language of the cosmetic chemist. It allows for agility in the lab—permitting substitutions and adjustments without compromising the safety or performance of the final cosmetic. Remember: Where there is water, there must be a preservative.

55 thoughts on “Water in Cosmetic DIYs”

  1. Thank you for your posts and sharing. I still have to learn a lot about making creams… As you said, water is a problem for preserving them. To avoid these problems with the water, what do you think about making a cream only with oils, butters and waxes and a tonic to use previous to the face cream with the soluble components?
    Many thanks!!!

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    1. The problem would be that it wouldn’t be a cream but an ointment 😉
      A cream, to be a “cream”, needs oils, water and an emulsifier (and consequently a preservative as well) 😉

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    2. One more thing to WHY a real cream is better than the use of two separated phases on the skin used one after the other:
      it has been proven that using emulsified phases (like those in a proper cream) keeps the skin more hydrated than doing otherwise. 🙂
      Just use a REAL (vitamin E is NOT a preservative, nor is vitamin C), certified, eco-not-unfriendly preservative and you will be great 😉

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      1. Thanks!!! I have tried grapefruit extract as a preservative (hydroalcoholic extract), but I think that it was not very effective.

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  3. Glad to read that you don’t use Vit E or grapefruit as a preservative. Even my supplier states both as preservatives. No sign of the word antioxidant only preservative.

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    1. I would change supplier: if they sell stuff they don’t even know about, that means they are not knowledgeable in what they do.
      There are many many suppliers in the entire world! 🙂

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  4. Hello,

    I’m appreciated your articles from your website. They really help me a lot!
    And I’d like to know, if it’s okay to use the filtered water (I have a filtering machines at home, which has a faucet that can filters the water and I can drink directly) for my homemade cosmetic products?

    Thank you?

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  5. Hi,

    Thanks for this post. What if I wanted to make 16 ounces of product? How would I calculate this?

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  6. Is boiling demineralized water in a metal pot safe? I mean – can it interact somehow during boiling?

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      1. I don’t know what type of pots people usually use in other countries, but it’s just a standard stainless pot 😛 It’s quite old with scratches (it’s not rusty) on the bottom.

        I read that boiling in glass, which is placed in the pot with water isn’t actually boiling, because temperature of glass is to low to make water in glass evaporate.

        I read a topic where specialist, which deals with water 20+ years, wrote that boiling water in a pot made of aluminium/stainless steel might make the water dissolve a few parts per million of the metal.
        These are very small amounts for me, it’s like homeopathy 😀 – so boiling in the metal pot shouldn’t be a big problem, IMO.

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      4. Ps. I have both boiled in glass and in metal. Companies that produce cosmetics use demineralized purified water but work mostly in stainless steel. So I don’t see the issue either 😉

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  7. Hi is AMTicide coconut combine with leucidal SF maw safe enough to prevent all type of contamination in the cream?

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    1. I am not sure as it should be tested and I don’t have data on this combination, sorry.
      However, contamination is prevented with proper GMP (good manufacturing practices), good packaging that makes the contamination difficult and THEN also a good preserving system that protects against bacteria and molds combined.

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