How much bleach do you put in a gallon of water to make it drinkable?

For unscented household bleach at 6 per cent sodium hypochlorite, the EPA says 8 drops per gallon of clear water; at 8.25 per cent, 6 drops. The CDC gives 8 drops per gallon for bleach in the 5 to 9 per cent range, which is about half a millilitre, a little less than an eighth of a teaspoon. Double it if the water is cloudy, coloured or very cold, stir, and let it stand 30 minutes. If it does not smell faintly of chlorine, repeat the dose and wait another 15 minutes.

Does boiling or bleach remove chemicals from water?

No. The EPA's own wording is that these methods will not destroy other contaminants such as heavy metals, salts and most other chemicals. Disinfection is about germs. If you suspect fuel, solvents, pesticides or industrial contamination, treatment at home is not the answer and boiling can concentrate rather than remove some of it.

chapter 03 · water & home · part 8 of 9 · field note · 11 September 2026

Filter, treat, test: the exact dose for the water you actually have

Q: How long do you boil water to make it safe?

One minute at a rolling boil, then let it cool. The two federal sources disagree on where the altitude rule kicks in: the EPA says boil three minutes above 5,000 feet, the CDC says above 6,500 feet. We use the lower threshold on this page, because the cost of an extra two minutes of boiling is nothing and the cost of being wrong is not.

Q: What should I test my well water for, and how often?

The EPA recommends testing a private well every year for total coliform bacteria, nitrates, total dissolved solids and pH, and more often where there are small children, older adults or anyone pregnant or nursing in the house. After a flood, disinfect the well and then test it, and contact your state or local health department, which in many places will test for free.

Everything earlier in this chapter ends here. The roof catches water, the tank stores it, the air holds it, and none of that matters until the water is safe to drink. Making it safe is three separate jobs, and almost every product on the market does one of them while sounding like it does all three. This page gives you the federal dose for the container in front of you, the waiting time, and the plain list of what none of it removes.

the dose

What to add, to this much water, and how long to wait

Pick the container and what you have in the cupboard. Every figure below is the federal per-gallon dose multiplied by your volume; nothing here is our own recipe. Read your bleach label first, because the concentration decides the dose and the two common strengths need different amounts.

How much water Or type your own number below. A full bathtub is roughly 40 gallons, and a 55-gallon drum is the usual barrel.

Your own number, in gallons Used only when the box above is set to "Type my own".

What you have Boiling is first for a reason: the CDC says chemical disinfectants do not work as well as boiling against Cryptosporidium and Giardia.

The water looks Cloudy, coloured or very cold water takes twice the chemical dose. Let it settle and pour it through a clean cloth or a coffee filter first either way.

Where you are The EPA puts the line at 5,000 feet and the CDC at 6,500. We use the lower one.

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what to add

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or, in other units

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before you drink it

Sources: EPA, "Emergency Disinfection of Drinking Water" (page dated 24 February 2026) for the 6 and 8.25 per cent bleach doses, the calcium hypochlorite and iodine methods, the 30-minute wait and the one-minute boil with three minutes above 5,000 feet. CDC, "How to Make Water Safe in an Emergency" (page dated 19 September 2024) for the 5 to 9 per cent and 1 per cent bleach doses, the filter pore sizes and the note about Cryptosporidium and Giardia. Both read on 11 September 2026. The only arithmetic here is multiplying the published per-gallon dose by your volume, using the CDC's own equivalence of 8 drops to half a millilitre.

three jobs, not one

Clear, kill, remove. Most gear does one.

Clear it. Letting water settle and pouring it through a clean cloth, a paper towel or a coffee filter is the step people skip, and it is the one that makes the next step work. Particles shelter germs from chlorine, which is exactly why the dose doubles for cloudy water.

Kill what is alive. Boiling, chlorine, iodine and chlorine dioxide all do this, and they are not equal. The CDC is blunt that chemical disinfectants do not work as well as boiling against Cryptosporidium and Giardia, and blunter still about the parasite: iodine and ordinary chlorine tablets will not kill Cryptosporidium, while chlorine dioxide tablets will if the instructions are followed. A portable filter does the job mechanically instead, and the size is the specification that matters: an absolute pore of 0.3 microns or smaller for bacteria, 1 micron or smaller for parasites.

Remove what is dissolved. This is the job almost nothing in a bug-out bag does. In the EPA's own words, these methods will not destroy other contaminants such as heavy metals, salts and most other chemicals. Boiling concentrates them. If you suspect fuel, solvent, pesticide or industrial contamination, the answer is a different water source, not a longer boil.

A label that says "purifier" is a marketing word, not a standard. The numbers that mean something are the pore size, the concentration on the bleach bottle and the contact time.

when two federal pages disagree

Five thousand feet, or six and a half thousand?

Boil for one minute. Above a certain altitude, boil for three, because water boils cooler where the air is thinner. The EPA's emergency disinfection page puts that line at 5,000 feet. The CDC's puts it at 6,500 feet. Both pages are current, both are federal, and they do not agree.

We use 5,000 feet. Not because the EPA is more right, but because the two extra minutes cost a little fuel and the error in the other direction costs something that matters. Where a source is uncertain, the site's rule is to pick the safer number and say out loud that we did.

The same reading applies to the chlorine smell. The EPA says treated water should have a slight chlorine odour, and if it does not, repeat the dose and wait another fifteen minutes. That instruction exists because the first dose can be entirely consumed by whatever is in the water, which is a signal, not a failure of the bleach.

the doses, in one table

Per gallon of clear water, double if cloudy

Method	Per gallon, clear	Wait	Source
Boiling	1 minute rolling	cool it	EPA and CDC; 3 minutes above 5,000 ft (EPA)
Bleach, 5 to 9 per cent	8 drops	30 min	CDC, about 0.5 mL
Bleach, 6 per cent	8 drops	30 min	EPA
Bleach, 8.25 per cent	6 drops	30 min	EPA
Bleach, 1 per cent	40 drops	30 min	CDC, about 2.5 mL or ½ tsp
Tincture of iodine, 2 per cent	20 drops	30 min	EPA, 5 drops per quart
Calcium hypochlorite solution	1 part per 100	30 min	EPA, 1 pint per 12.5 gallons
Chlorine dioxide tablets	read the packet	read the packet	CDC; the one chemical that handles Cryptosporidium

Sources: EPA, "Emergency Disinfection of Drinking Water", page dated 24 Feb 2026; CDC, "How to Make Water Safe in an Emergency", page dated 19 Sept 2024. Both read 11 Sept 2026. Iodine per gallon is the EPA's per-quart figure multiplied by four, which is the only conversion in the table.

the part nobody does

Testing, which is the only step that answers the question

Treating water tells you what you did to it. Testing tells you what was in it. For a private well the EPA's recommendation is an annual test for total coliform bacteria, nitrates, total dissolved solids and pH, and more often in a house with small children, older adults, or anyone pregnant or nursing. That is four numbers a year, and most well owners have never had one.

After a flood the order is fixed: disinfect the well, then test it, then wait for the result before drinking. Your state or local health department is the place to start, and in many counties the test is free or close to it. On city water, the equivalent is your utility's annual Consumer Confidence Report, which is a published document about the water leaving the plant and not about what happened to it in your building's pipes.

None of this is fast, which is the honest reason people skip it. Treat the water in front of you today; book the test this week.

the official sequence

Disinfect the well, then test it, then wait

This is a state health department walking through the order for a private well: disinfect with bleach, test, and do not drink until the result comes back. It is their work, shown here with their embed enabled, and their instructions apply to their state's guidance, not ours.

Video by an agency we don't own

"Disinfect Your Private Well (with Bleach) Before Testing" by the North Carolina Department of Health and Human Services on YouTube. Their guidance for their state. Follow your own health department where the two differ.

chapter 03 · water at homenine parts, read in any order

i.How much water your house needs, and the Water Freedom System review
ii.Rain barrel calculator, by state
iii.48 hours without power: a small apartment's quiet plan
iv.A 30-day pantry, priced with this month's numbers
v.Generator vs. battery: what your state's outages say
vi.Water from air, explained by the humidity where you live
vii.This week's drought map, and your plan on top of it
viii.Filter, treat, test: making stored water drinkable
ix.The blackout kit you already own

Next: part ix, the blackout kit already in your house.Read part ix →

straight answers

Questions people ask

How much bleach do you put in a gallon of water?

Eight drops of unscented 6 per cent bleach, or six drops at 8.25 per cent, for a gallon of clear water. The CDC gives the same 8 drops for anything in the 5 to 9 per cent range, about half a millilitre. Double it for cloudy, coloured or very cold water, stir, wait 30 minutes, and check for a faint chlorine smell.

How long do you boil water to make it safe?

One minute at a rolling boil, three minutes at altitude. The two federal pages disagree about where altitude starts, 5,000 feet on the EPA's and 6,500 on the CDC's, so this page uses the lower one and says so.

Does boiling or bleach remove chemicals?

No. The EPA's wording is that these methods will not destroy other contaminants such as heavy metals, salts and most other chemicals. Boiling concentrates them rather than removing them. Suspected fuel, solvent or industrial contamination is a reason to find another source, not to boil longer.

Will a filter or tablets handle Cryptosporidium?

Iodine and ordinary chlorine tablets will not, according to the CDC. Chlorine dioxide tablets will, if the packet instructions are followed. A portable filter handles it mechanically when the absolute pore size is 1 micron or smaller; 0.3 microns or smaller is the figure for bacteria.

What should I test a well for, and how often?

Every year, for total coliform bacteria, nitrates, total dissolved solids and pH, per the EPA, and more often with small children, older adults or anyone pregnant or nursing in the house. After a flood, disinfect first, then test, then wait for the result before drinking.

Last updated: 11 September 2026. Doses and waiting times are the EPA's and the CDC's, with the page dates shown. This is general guidance, not medical or engineering advice, and a local boil-water notice overrides anything here.

How we stay honest: every dose, waiting time and pore size on this page is the EPA's or the CDC's, quoted with the date on their page and the date we read it. The only arithmetic of ours is multiplying a published per-gallon figure by your container size, using the CDC's own drop-to-millilitre equivalence. Where the two agencies disagree we show both and say which one we follow and why. We recommend no product, we have tested none of these methods in a laboratory, and nothing here is medical, engineering or legal advice. Your local authority's boil-water notice outranks this page. The video belongs to the agency credited above.