How to Purify Water with Bleach: Exact Dosing
Bleach is the cheapest and most available emergency water disinfectant. Here is the exact CDC dosing protocol, what bleach kills, what it misses, and how to stockpile it correctly.
Why Bleach Is the Most Important Water Treatment Chemical to Stockpile
When municipal water fails after a hurricane, earthquake, or infrastructure attack, you have two problems: where to get water, and how to make it safe. Filtration gear handles the second problem well — but filters are expensive, can clog, and require maintenance. Bleach is different.
A standard 121-oz jug of unscented household bleach costs around $4. At the correct treatment dose, that single jug can disinfect roughly 3,800 gallons of clear water. Most households already own bleach. Most convenience stores stock it. It requires no power, no moving parts, and no special training — just a clean dropper and a timer.
That combination of low cost, wide availability, and simplicity is why the CDC and FEMA both name household bleach as the primary emergency water disinfection method for the general public. No other chemical treatment is as accessible or as proven.
There are real limits to what bleach does — it is not a complete water treatment system. But as a first-response tool and a stockpile staple, it is irreplaceable. Every preparedness kit should have it.
What Bleach Kills (and What It Does Not)
Sodium hypochlorite kills bacteria and viruses rapidly at the correct dose. This covers the most common waterborne threats after a disaster: E. coli, Salmonella, Shigella, Norovirus, and Hepatitis A.
What bleach reliably kills at standard dose:
| Pathogen Type | Example | Killed by Bleach? |
|---|---|---|
| Bacteria | E. coli, Salmonella, Cholera | Yes |
| Viruses | Norovirus, Hepatitis A | Yes |
| Giardia | Giardia lamblia | Partially (requires higher dose + time) |
| Cryptosporidium | Crypto oocysts | No |
The Cryptosporidium problem is critical to understand. Crypto oocysts have a hard shell that chlorine cannot penetrate at any dose you would add to drinking water. During flooding events — exactly when you might rely on bleach — Cryptosporidium contamination is common because animal feces wash into water supplies.
If Cryptosporidium is a realistic threat (flood-affected water, surface water from a lake or stream, water of unknown origin), bleach alone is not enough. Your options are:
- Boil the water — one minute at a rolling boil kills Crypto
- Use chlorine dioxide — the only chemical that kills Crypto, but requires 4 hours of contact time
- Filter first — a filter with a pore size of 1 micron or smaller (like the Sawyer Squeeze) physically removes Crypto before you add bleach
What bleach does not remove at all: heavy metals (lead, arsenic), industrial chemicals, pesticides, petroleum products, and sediment. For chemically compromised water — water that smells like fuel, chemicals, or industrial runoff — no disinfection method makes it safe. That water needs activated carbon filtration or should be avoided entirely.
The Right Bleach to Use
Not all bleach is suitable for water treatment. Get this wrong and you can make the water more dangerous, not less.
Use bleach that is:
- Unscented — scented bleach contains fragrances, surfactants, and other additives that are not safe to ingest
- Plain sodium hypochlorite only — the label should list sodium hypochlorite as the only active ingredient
- 6% to 8.25% sodium hypochlorite concentration — this is standard US household bleach (Clorox Regular, Kroger Original, store brands)
- No “splash-less,” “ultra,” or “concentrated” formulas with added thickeners or surfactants
Bleach to avoid:
- Splash-less bleach (contains thickeners)
- Bleach with “clean lemon” or any scent
- Pool shock (calcium hypochlorite — different chemistry, different dosing)
- Industrial bleach above 8.25% concentration
The most common brands — Clorox Regular-Bleach and store-brand equivalents in the white jug labeled “regular” — are correct. When in doubt, check the label: it should read 6% or 8.25% sodium hypochlorite and list no other active ingredients.
Exact Dosing Table
The CDC and EPA use this protocol. These doses assume standard household bleach at 6% to 8.25% sodium hypochlorite.
Clear Water (pre-filtered or visually clear)
| Water Volume | 6% Bleach | 8.25% Bleach |
|---|---|---|
| 1 liter | 2 drops | 2 drops |
| 1 quart (about 1 liter) | 2 drops | 2 drops |
| 1 gallon | 8 drops | 6 drops |
| 5 gallons | 40 drops (about 1/2 tsp) | 30 drops |
| 10 gallons | 80 drops (about 1 tsp) | 60 drops |
| 55-gallon drum | 1 cup | 3/4 cup |
Cloudy or Turbid Water (double the dose)
| Water Volume | 6% Bleach | 8.25% Bleach |
|---|---|---|
| 1 liter | 4 drops | 4 drops |
| 1 gallon | 16 drops | 12 drops |
| 5 gallons | 80 drops (about 1 tsp) | 60 drops |
| 10 gallons | 160 drops (about 2 tsp) | 120 drops (about 1.5 tsp) |
Converting drops to teaspoons and tablespoons:
- 20 drops = approximately 1 mL
- 100 drops = approximately 1 teaspoon (5 mL)
- 300 drops = approximately 1 tablespoon (15 mL)
For large-volume treatment (5 gallons or more), measuring drops is impractical. Switch to fractions of a teaspoon using a clean measuring spoon. A standard medicine dropper or eyedropper dispenses approximately 20 drops per mL — useful to know when calibrating your kit.
Step-by-Step Treatment Process
Step 1: Pre-treat turbid water
If your water source is visually cloudy, silty, or discolored, you must reduce the turbidity before chemical treatment. Suspended particles physically shield pathogens from chlorine contact — adding bleach to muddy water does not make it safe.
To pre-treat turbid water:
- Let the water sit undisturbed for 30 minutes to allow heavy sediment to settle
- Carefully pour the clearer water off the top into a clean container, leaving the settled sediment behind
- Pour that water through a clean cloth, bandana, or coffee filter to remove remaining particles
- Repeat the settling and filtering step until the water is as clear as you can get it
- Proceed with chemical treatment at the cloudy-water dose (double the standard amount)
Step 2: Add bleach
Use a clean dropper, medicine dispenser, or measuring spoon. Add the correct dose based on your water volume and clarity from the table above. Stir or cap and shake the container to mix the bleach thoroughly throughout the water.
Step 3: Wait 30 minutes
This is not optional. Chlorine needs contact time to kill pathogens. Do not drink the water during the contact period.
For cold water (below 40 degrees Fahrenheit), extend the wait time to 60 minutes. Cold water slows the chlorine reaction significantly.
Step 4: The chlorine smell test
After 30 minutes, open the container and smell the water. Treated water should have a faint but detectable chlorine smell — similar to a lightly chlorinated swimming pool.
- Faint chlorine smell: Treatment is complete. Water is safe to drink.
- No chlorine smell at all: The dose was insufficient for the contamination level. Repeat the same dose and wait another 15 minutes. If still no smell, the water may have very high organic content — pre-filter more thoroughly and try again.
- Strong, overwhelming chlorine smell: You added too much. Let the water sit uncovered for a few hours, or pour it back and forth between containers to off-gas excess chlorine. It is not harmful at twice the treatment dose, but the taste is unpleasant.
Bleach Shelf Life: What You Need to Know
Bleach is not a stable compound. Sodium hypochlorite gradually breaks down into salt and water — a process that accelerates with heat, light, and exposure to air.
General degradation rate:
- Stored at room temperature (around 70 degrees Fahrenheit): loses roughly 20% potency per year
- Stored warm (above 85 degrees Fahrenheit, like a garage in summer): loses roughly 50% potency in 6 months
- Stored cool and dark (below 60 degrees Fahrenheit): degrades more slowly, approaching full potency for 18-24 months
Practical rule: Rotate your bleach supply annually. When you buy a new jug, write the purchase date on it with a marker. Use the oldest stock first.
What happens when bleach degrades: A bottle of bleach that has lost half its potency does not stop working — it just requires twice the dose to achieve the same kill rate. If your bleach is more than a year old, double the dose listed in the table above and extend the contact time to 60 minutes. The faint-smell test still applies.
Commercially bottled chlorine tablets (pool shock, NaDCC tablets) have substantially better shelf life than liquid bleach and are worth considering for long-term stockpiling. But liquid bleach remains the most accessible and versatile option for most households.
How Much Bleach to Stockpile
The EPA recommends storing 1 gallon of water per person per day for a minimum of 3 days (14 days is more realistic for serious preparedness). For a family of four over 14 days, that is 56 gallons of water.
Treating 56 gallons of clear water at the standard dose (8 drops per gallon of 6% bleach) requires 448 drops — about 4.5 teaspoons of bleach, or roughly 22 mL. A single 30-oz bottle of bleach contains around 890 mL. That means one standard bottle can treat approximately 1,600 gallons of clear water at the basic dose.
For a realistic preparedness stockpile:
| Scenario | Gallons Needed | Bleach Required |
|---|---|---|
| 1 person, 14 days | 14 gallons | Less than 1/4 teaspoon |
| Family of 4, 14 days | 56 gallons | About 1 teaspoon |
| Family of 4, 3 months | 360 gallons | About 2 tablespoons |
| Family of 4, 1 year | 1,460 gallons | About 1/2 cup |
The math shows bleach goes an extremely long way. Even accounting for degradation, two or three 30-oz bottles of unscented bleach represent a multi-year water treatment supply for a family of four — at a total cost of under $10.
The practical stockpile recommendation: keep four to six 30-oz bottles of unscented bleach in your preparedness supplies, rotated annually. This covers water treatment and leaves enough for sanitation uses (surface disinfection, flood cleanup).
What Bleach Cannot Do
Bleach is a disinfectant. It is not a purifier in the full sense. Know the limits:
Heavy metals and inorganic chemicals: Bleach has no effect on lead, arsenic, nitrates, fluoride, or other inorganic contaminants. Water from a flooded industrial area, near mining operations, or from old plumbing with lead pipes needs activated carbon filtration or should not be used for drinking.
Sediment and turbidity: Bleach does not remove particles, silt, or debris. You must pre-filter turbid water before chemical treatment — not after.
Chemical contamination: Fuel, pesticides, solvents, and industrial byproducts are not affected by chlorine. If the water smells like chemicals, looks oily, or comes from a source near industrial activity, bleach treatment is not sufficient.
Taste and odor beyond chlorine: Bleach will not improve bad tastes caused by algae, sulfur, iron, or tannins in the water. A carbon filter (even a Brita pitcher) removes most taste and odor issues after disinfection.
Double Treatment: Maximum Safety Protocol
For the highest confidence in treated water — particularly when the source is unknown, potentially flood-contaminated, or may involve Cryptosporidium — use bleach as the first step in a two-stage protocol:
- Pre-filter to remove sediment and particles
- Treat with bleach at the appropriate dose and wait 30 minutes
- Follow with UV treatment (SteriPEN or equivalent) or boil the water for one minute
The bleach step kills bacteria and viruses rapidly. The UV or boiling step kills any Cryptosporidium that bleach missed. Together, the two steps cover every biological waterborne threat.
This double-treatment approach is especially worthwhile during flooding events, when Cryptosporidium and chemical runoff are both elevated risks. It takes an extra 10 minutes but gives you high confidence in the water regardless of the source.
For ongoing use with a known-good water source (a sealed well, municipal tap water of uncertain status, or rainwater collected from a clean surface), single bleach treatment at the correct dose and contact time is reliable.
Quick Reference Card
The 4 things to remember:
- Bleach: Unscented, 6-8.25% sodium hypochlorite only
- Dose: 8 drops per gallon (clear water) — 16 drops per gallon (cloudy water)
- Wait: 30 minutes minimum — 60 minutes in cold water
- Test: Faint chlorine smell = safe. No smell = repeat the dose.
For broader context on choosing between bleach, tablets, and filters for your emergency kit, see water purification methods. For tablet-based chemical treatment options including chlorine dioxide (the only chemical that kills Crypto), see water purification tablets. For container selection and long-term water storage strategy, see emergency water storage.
Frequently Asked Questions
How much bleach do you add to water to purify it?
For clear water, add 8 drops of unscented 6-8.25% sodium hypochlorite bleach per gallon, or 2 drops per liter. For cloudy water, double the dose to 16 drops per gallon. Wait 30 minutes before drinking. The treated water should have a faint chlorine smell — if it does not, repeat the dose and wait another 15 minutes.
Does bleach kill Cryptosporidium in water?
No. Bleach (sodium hypochlorite) does not reliably kill Cryptosporidium at any practical dose. Cryptosporidium oocysts are highly resistant to chlorine. To kill Crypto, you must either boil the water (1 minute at a rolling boil) or use chlorine dioxide tablets with a 4-hour contact time.