The short version
- Sanitising is the step after cleaning, never a substitute for it.
- 100–200 ppm free chlorine, ten minutes, all surfaces wetted including the valve.
- Drain through the outlet so the throat and valve body get treated too.
- It does not treat the water you put in afterwards — that is a separate problem.
What sanitising is and is not
Cleaning removes soil. Sanitising reduces the microbial population on an already-clean surface. They are sequential steps and the second one does not work without the first — chlorine is consumed rapidly by organic matter, so sanitising a dirty container mostly produces chlorinated dirty water.
This matters because we issue wash certificates and people occasionally read them as more than they are. A wash certificate says the container was cleaned on a specific line by a specific process on a specific date. It says nothing about microbial load, and it does not travel with the container into whatever you do next.
The other thing sanitising is not: water treatment. A sanitised container holding untreated roof runoff still contains untreated roof runoff. If you intend to drink it, the water itself needs filtration and disinfection engineered for the purpose. Sanitising the vessel is necessary and nowhere near sufficient.
Before you start: three prerequisites
- A Grade A food-safe container with a documented single food-contact prior product. Not an industrial container, not one with an unknown history, and not one that has been used for anything else in between. This is not negotiable and no procedure fixes it.
- A completed clean. Either our food-line wash with a certificate, or a thorough triple rinse you performed yourself. Visibly clean, no residue, no odour.
- A new EPDM gasket fitted and the valve either new or verified. A gasket that has been compressed for two years holds residue in the compressed face where nothing reaches.
The procedure
Make up the solution
Unscented household bleach at roughly 5–6% sodium hypochlorite. For 100–200 ppm free chlorine, about 1.5 to 3 fluid ounces of bleach per 100 gallons of water. There is no benefit to going stronger; above roughly 200 ppm you are adding rinse burden and attacking the gasket, not adding efficacy.
Fill to about a quarter and wet every surface
Cap the lid, then rock the container on a forklift or roll it if you can. Every internal surface needs contact, including the top panels and the shoulders. A container standing still with solution in the bottom quarter has sanitised the bottom quarter.
Hold ten minutes minimum
Contact time is doing the work. Ten minutes at 100–200 ppm is the standard figure. Longer does no harm within reason; shorter does not achieve the reduction you are assuming.
Drain through the outlet, not the lid
This is the step people skip and it matters more than it sounds. Draining through the outlet pushes solution through the valve body and the outlet throat, which are otherwise the two least sanitised parts of the container and the two closest to your dispensing point.
Rinse with potable water until the odour is gone
Two to three full fill-and-drain rinses with potable water, draining through the outlet each time. Chlorine odour is a reasonable practical endpoint; test strips are better if you have them, aiming for under 0.5 ppm residual.
Dry or fill promptly
Either air dry with the lid off under cover, or fill straight away. A damp sealed container left for a week undoes the work.
Record what you did
Date, concentration, dwell, who did it, container unit number. If anyone ever asks — a health inspector, a customer, an insurer — the record is the answer. Undocumented sanitising is indistinguishable from no sanitising.
Peracetic acid, and why we mostly use it
Chlorine is cheap, universally available and effective, which is why the procedure above is written around it. On our own line we generally use peracetic acid instead, at label strength, and it is worth knowing why.
| Chlorine (hypochlorite) | Peracetic acid | |
|---|---|---|
| Cost | Very low | Moderate |
| Availability | Anywhere | Chemical supplier |
| Rinse burden | High — needs 2–3 rinses | Low — decomposes to acetic acid and water |
| Odour carry-over | Common if under-rinsed | Minimal |
| Effect on EPDM | Degrades with repeated use | Gentler |
| Effective at low temperature | Yes | Yes |
| Handling hazard | Moderate | Higher — concentrate is aggressive |
For a one-off container in a back lot, chlorine is the right answer. For a line doing it repeatedly, peracetic acid saves enough rinse water and enough gasket replacement to be worth the handling care it demands.
And then keep the light out
A perfectly sanitised container full of clean water, standing in daylight, will grow algae. Translucent HDPE plus light plus any nutrient load at all is a reliable recipe, and in warm weather it takes two to four weeks.
A UV-opaque cover is $48 and it is the difference between a potable store you can use in September and one you have to empty in July. For emergency water stores in particular — municipalities, fire stations, community groups — cover the containers and rotate the water on a schedule. Six months is a sensible interval; twelve is pushing it.
Written by Priya Raghunathan, wash chemistry & compliance at IBC Totes San Francisco. Published September 25, 2025. Spotted something wrong? Tell us — we would rather fix it than defend it.