Water binding reduces the water activity in a product that contains water, so it requires less preservation as the bound water isn’t available for microbes to grow. This is part of the process of hurdle technology the we follow to reduce the growth of microbes in our products that contain water.
It can also offer our skin more hydration because the ingredients that bind water also work as great humectants to draw water to our skin and to be trapped against our skin for longer periods of time.
Water activity is defined as the water requirements for survival or growth of micro-organisms. It’s a measure of the amount of free (unbound or active) water molecules present in our products.
It’s measured like this – 1.0 would be loads of unbound water. 0.75 means there’s quite a lot of bound water.
Reducing the water activity of the product is super important. If we can bind the water with ingredients like glycerin, propylene glycol, propanediol 1,3, hexylene glycol, and other glycols, there’s less available for nasty beasties to use to multiply.
We can’t really test for water activity in our workshops – the device I was looking at was over $8,000 Canadian – but we can do our best to limit it when we are making products, like adding more water binding ingredients in a lotion, especially when we’re using unconventional preservatives or “naturally compliant” ones.