The bleach disinfection ratio everyone gets wrong

Why the ratio changed

Clorox and most major bleach manufacturers reformulated their standard household bleach from 6% sodium hypochlorite to 8.25% around 2013 to 2014. The higher concentration provides more disinfection power per ounce, allows smaller package sizes, and extends effective shelf life. The formulation change was industry-wide and is now the standard for regular-strength household bleach across all major brands.

The CDC updated its emergency water disinfection guidance accordingly. Many preparedness guides, emergency management documents, and well-intentioned online resources still cite the pre-2014 formula. The discrepancy is persistent because the older documents remain indexed and circulated, and because neither formula produces visibly different results in the water — the difference only matters for the actual disinfection outcome.

The current CDC guidance — verified

How to identify your bleach concentration

The sodium hypochlorite concentration is on the label of every bleach bottle — usually on the back, in the active ingredients section. Standard household bleach sold in the US today reads 8.25% sodium hypochlorite. Concentrated bleach (marketed as "ultra" or "concentrated" in some older formulations) may be higher — 10% or more — and should not be used for water disinfection without adjusting the dose accordingly.

Splashless bleach, scented bleach, and bleach with added surfactants or cleaning agents are not appropriate for water disinfection. Only unscented, plain sodium hypochlorite bleach should be used. The label should list no additives beyond sodium hypochlorite and water.

Bleach loses potency over time. A bottle of bleach older than six months may have degraded from its labeled concentration — particularly if stored in warm conditions. For emergency water treatment, use bleach purchased within the past six months if possible. If older bleach is all you have, increase the dose modestly and confirm the chlorine smell after the treatment wait period.

What bleach treatment does and does not do

Bleach disinfection kills or inactivates most bacteria and viruses that cause waterborne illness — including E. coli, Salmonella, Hepatitis A, and enteric viruses. It does not remove chemical contamination, heavy metals, PFAS, sediment, or protozoa like Cryptosporidium. For Cryptosporidium specifically, boiling or a certified 1-micron absolute filter is required — sodium hypochlorite at drinking water treatment doses does not reliably inactivate it.

For field water from uncertain biological sources — standing water, stream water, rain barrel water — the recommended approach is pre-filter through a mechanical filter (Sawyer Squeeze, etc.) to remove protozoa and bacteria, then chemically disinfect with bleach or purification tablets to address viruses. The combination covers the full biological range that disinfection tablets and filters address individually.

What to do right now

1. 1 Check the bleach concentration on your current bottle. Look for the sodium hypochlorite percentage in the active ingredients. If it is 8.25%, the current dose is 6 drops per gallon. If it is 6%, the dose is 8 drops.
2. 2 Write the correct ratio on your bleach bottle in permanent marker. When you need this information, you will not want to search for it. A note directly on the bottle removes that step.
3. 3 Keep unscented bleach in your emergency supplies and rotate it every six months. Use the old bottle for household cleaning — do not store bleach for emergency water treatment that is more than six months old.
4. 4 Keep purification tablets as a backup. Potable Aqua and Aquamira are pre-measured, shelf-stable for four years, and require no measuring. For an emergency kit, tablets are simpler than calculating and measuring bleach drops under stress.