I preserve anything I add water to. But I've seen some videos on YouTube from a cosmetic chemist saying that if a formula has 5% or less of water that a preservative is not required because the water activity is low enough to not be a concern. I was a bit confused because I thought that water activity couldn't be accounted for accurately without specialized equipment. If anyone could shed some light on the 5% or less, I'd appreciate any insights. Thank you!