What is the correct bleach to water ratio for disinfecting surfaces?

The CDC recommends 5 tablespoons (one-third cup) of regular unscented household bleach per gallon of room-temperature water for hard, non-porous surfaces like counters, sinks, and floors. This produces a solution of approximately 1,000 parts per million of sodium hypochlorite. Apply the solution and keep the surface visibly wet for at least one minute, then allow it to air dry.

Is 50/50 bleach and water too strong for cleaning surfaces?

Yes. A 50/50 mixture of bleach and water is dangerously concentrated for routine surface cleaning. It produces fumes that irritate the eyes and lungs, can damage surfaces, and wastes bleach that may be irreplaceable during a disruption. The CDC ratio is 5 tablespoons per gallon, which is roughly 1 part bleach to 80 parts water. More is not better.

Can I use bleach to sanitize food preparation surfaces?

Yes, but at a lower concentration than general surface disinfection. Use 1 tablespoon of unscented bleach per gallon of water for food-contact surfaces. Apply, keep the surface wet for at least one minute, then rinse with clean water and allow to air dry. This is the same approach used in commercial food service.

How long does a mixed bleach solution last?

A diluted bleach solution is effective for about 24 hours. After that, the chlorine degrades and the solution loses disinfecting power. Mix only what you need for the day. Store unmixed bleach in its original container, in a cool dark place, and check the expiration date. Expired bleach may not disinfect effectively.

Surface Disinfection During Disruptions — Water

The problem

Surface cleaning is not water treatment

The NWS Bleach Water Disinfection guide covers the EPA protocol for treating drinking water: 8 drops per gallon for clear water, 16 drops for cloudy. That page saves lives. This page covers a different use: disinfecting the surfaces your household touches, eats from, and sleeps near during an extended disruption.

The ratios are not the same. Water treatment uses drops. Surface disinfection uses tablespoons. Mixing them up in either direction is a problem: too weak fails to disinfect, and too strong produces fumes that irritate your lungs, damages surfaces, and wastes bleach you may not be able to replace.

A ratio that circulates in some preparedness circles is 50/50 bleach and water. This is roughly 40 times stronger than the CDC recommendation. It produces dangerous fumes in enclosed spaces and is never appropriate for household surface cleaning.

The CDC ratios

Two ratios. One for surfaces, one for food areas.

Hard surfaces

5 tablespoons (1/3 cup) bleach per 1 gallon of water

Counters, sinks, bathroom fixtures, door handles, light switches, shared tools, hard flooring. Apply the solution with a cloth or spray bottle. Keep the surface visibly wet for at least 1 minute. Allow to air dry.

Equivalent: 4 teaspoons per quart. Approximately 1,000 ppm sodium hypochlorite.

Food-contact surfaces

1 tablespoon bleach per 1 gallon of water

Cutting boards, plates, utensils, food preparation areas. Apply the solution, keep the surface wet for at least 1 minute, then rinse with clean water and allow to air dry. This is the standard concentration used in commercial food service.

Approximately 200 ppm sodium hypochlorite.

Which bleach to use

Regular, unscented liquid household bleach containing 5 to 9 percent sodium hypochlorite. Do not use color-safe bleach, splashless bleach, or bleach with added fragrances or surfactants for disinfection. Check the percentage on the label. Check the expiration date. Expired bleach may not disinfect effectively.

How to do it right

Clean first, then disinfect

Disinfecting a dirty surface does not work. Dirt, grease, and food residue shield germs from the bleach solution and consume the active chlorine. The process is always two steps: clean with soap and water first, then apply the bleach solution.

Wash the surface with soap and water

Remove visible dirt, grease, and food residue. A dish soap solution and a clean cloth are sufficient. Wipe or rinse away the soap.

Apply the bleach solution

Use a spray bottle or a clean cloth soaked in the solution. Cover the surface completely.

Keep the surface wet for at least 1 minute

Contact time is what kills germs. A quick wipe and immediate dry-off does not disinfect. The surface needs to stay wet through the full contact period.

Air dry (food-contact: rinse first, then air dry)

Non-food hard surfaces can air dry without rinsing. Food-contact surfaces should be rinsed with clean water after the contact period, then air dried.

Safety rules

What not to do with bleach

Never

Mix bleach with ammonia or any other cleaner

Mixing bleach with ammonia produces chloramine gas. Mixing bleach with acids (vinegar, some toilet bowl cleaners) produces chlorine gas. Both are toxic and can cause serious respiratory injury in an enclosed space. Bleach goes with water. Nothing else.

Never

Use hot water to mix the solution

Hot water breaks down sodium hypochlorite faster, reducing the solution's disinfecting power. Use room-temperature water.

Never

Keep mixed solution longer than 24 hours

Diluted bleach loses its disinfecting power within a day. Mix what you need for today and discard the rest. Unmixed bleach in its original bottle lasts much longer, but check the expiration date.

Never

Use bleach on porous materials and expect disinfection

Bleach works on hard, non-porous surfaces: counters, tile, glass, sealed wood, metal, and plastic. It does not effectively disinfect fabric, carpet, unsealed wood, or drywall. For porous materials that are contaminated, removal and replacement is more effective than bleach treatment.

Ventilate while using bleach

Open a window or door in the room where you are disinfecting. Bleach solutions produce fumes that irritate eyes and airways, especially in enclosed spaces during a power outage when ventilation is already limited. If you feel lightheaded, leave the area and get fresh air.

During extended disruptions

What to disinfect and how often

During a normal day, your household immune system is supported by running water, regular handwashing, and a functional waste disposal system. During an extended outage, those supports weaken. Surface disinfection fills part of the gap. Focus on the surfaces that carry the most contamination risk.

Food preparation surfaces Before and after each meal prep

Shared eating surfaces After each meal

Bathroom fixtures (sink, toilet seat) Once daily

Door handles and light switches Once daily if anyone is ill, otherwise as needed

Shared tools and devices After shared use

This is not about sterilizing your home. It is about maintaining the hygiene baseline that running water normally provides. In a 14-day outage, a daily wipe-down of food prep and bathroom surfaces with the correct bleach solution is the single most effective thing you can do to prevent gastrointestinal illness in your household.

Sources

References

CDC. "Cleaning and Disinfecting with Bleach." 5 tablespoons (1/3 cup) per gallon for hard surfaces. Surface wet for at least 1 minute. Never mix with ammonia. cdc.gov
FDA. Food-contact surface sanitizing: 1 tablespoon bleach per gallon of water, 200 ppm sodium hypochlorite.
CDC. "Cleaning and Disinfection for Community Facilities." Two-step clean-then-disinfect process, 24-hour solution shelf life, ventilation during use.

The right ratio. Not the one you heard.

Surface cleaning is not water treatment

Two ratios. One for surfaces, one for food areas.

Clean first, then disinfect

What not to do with bleach

What to disinfect and how often

Keep reading

References