Water is the largest raw material by weight in most creams, lotions and essences, and the one buyers inspect least. A loop that wanders between 1 and 8 microsiemens per centimetre, or one that has not been sanitised since the last shutdown, will show up months later as a batch that fails on microbial count for no obvious reason.
1. Why water is a raw material
A 60 percent water formula carries more water than every other ingredient combined. That water brings its own conductivity, microbial load and dissolved metals. Pharmacopoeia-grade purified water is usually produced on site by reverse osmosis followed by electrodeionisation or distillation, then stored in a circulated stainless loop rather than in tanks.
2. The loop and the branches
Water is kept moving at roughly 1 to 2 metres per second to keep the surface under shear and to stop biofilm forming at the pipe wall. Branches that dead-end, or that are used once a week, are the usual source of contamination. A well-designed loop has no dead leg longer than about three pipe diameters.
3. Conductivity and the number that matters
Conductivity is the cheapest continuous signal available. Most plants alarm above 1.3 microsiemens per centimetre at 25 degrees, which corresponds to the usual purified water limit. Trend it rather than watching for alarms: a slow rise over two weeks usually means a resin bed or a membrane is exhausting.
4. Microbial control in a loop
Purified water is not sterile and is not required to be. The practical target is usually under 100 colony forming units per millilitre with no detected pathogens. Samples taken at the return leg and at the furthest point of use tell you different things, and taking only the return leg flatters the system.
5. Sanitisation frequency
Loops are typically sanitised with hot water above 80 degrees or with a chemical oxidiser on a fixed interval, often monthly. The interval should follow trend data, not habit. If counts climb in the two weeks before sanitisation, the interval is too long regardless of what the procedure says.
6. Sampling points that prove something
Sample at the generation outlet, the return leg, and the point of use furthest from the tank. Flush for a defined time before collecting, use sterile bottles, and plate within the holding time. A brand auditing a filler should ask to see twelve months of these three points, not a single certificate.
7. Stagnation and dead legs
Most excursions follow a shutdown. Water sits in branches, biofilm re-establishes at the wall, and the first batches after restart carry the highest counts. A restart procedure that flushes and re-samples before any product contact is worth more than an extra sanitiser dose afterwards.
8. What water does to a formula
Hardness and divalent metals affect more than microbial count. They can shift the pH of an acidic essence, interact with anionic thickeners, and dull a chelator’s effect on colour. If a formula behaves differently at two sites, check water before reformulating anything.
9. Questions for a factory tour
Ask how water is generated, where it is stored, how fast it circulates, when the loop was last sanitised, how many points of use exist, and whether the last three months of conductivity and bioburden trends can be shared. The answers are more informative than the equipment list on the wall.
10. Where it fits
Water-heavy formats include facial essences, body lotions and sheet mask serums. See the product range and encyclopedia notes on preservation.
