Chemicals and water treatment safety

This is a short reference for the household chemicals that are most useful (and most often misused) during a power or water outage. It covers safe disinfection of water that is only biologically contaminated, basic storage and handling rules, and the never-mix pairs that produce toxic gas. It also gives short, sourced notes on which common household chemicals are worth keeping, mold cleanup after a flood, fuel and propane storage, carbon monoxide, mosquitoes after storms, and where Charleston, Dorchester, and Berkeley County residents can take household hazardous waste. It does not cover industrial chemical releases, fuel or chemical contamination of water, or advanced DIY chemistry.

Always follow the instructions in an official alert or from local officials, even if they differ from the guidance here. If life is at risk, call 911.

Water disinfection for germs only

Boiling or chemical disinfection kills bacteria and viruses. It does not remove fuel, toxic chemicals, heavy metals, or radioactive materials. If you suspect chemical contamination, use stored bottled water and contact your local health department or utility. Do not try to treat it.

For water you believe is only biologically contaminated (and after filtering if it is cloudy):

Unscented household bleach (sodium hypochlorite, 5–8.25%)

Use only plain, unscented bleach with no added cleaners, fragrances, or color-safe additives. Check the label for the exact strength.

Bleach strength	Drops per gallon (clear water)	Notes
6%	8 drops	Double the amount if the water is cloudy, colored, or very cold
8.25%	6 drops	Same rule for cloudy, colored, or very cold water

Stir, wait 30 minutes, then check for a slight chlorine odor. If there is none, repeat the dose and wait another 15 minutes. Pour the water between two clean containers to reduce the taste if needed. Source: CDC and EPA.

Calcium hypochlorite (pool shock)

Dry calcium hypochlorite (typically 65–70% available chlorine) has a much longer shelf life than liquid bleach when kept dry and sealed. It is a concentrated oxidizer. Follow the manufacturer’s directions or a reliable official dosing chart for drinking-water use; do not guess. Store it in its original container, cool, dry, and away from acids, ammonia, and organic materials. See the never-mix list below.

EPA method for making drinking water with granular calcium hypochlorite, as stated by the EPA. The first step is to make a chlorine solution that you will use to disinfect your water.

For your safety, do it in a ventilated area and wear eye protection.
Add one heaping teaspoon (approximately ¼ ounce) of high-test granular calcium hypochlorite (HTH) to two gallons of water and stir until the particles have dissolved. The mixture will produce a chlorine solution of approximately 500 milligrams per liter.
To disinfect water, add one part of the chlorine solution to each 100 parts of water you are treating. This is about the same as adding 1 pint (16 ounces) of the chlorine solution to 12.5 gallons of water.
If the chlorine taste is too strong, pour the water from one clean container to another and let it stand for a few hours before use.

Caution (EPA): HTH is a very powerful oxidant. Follow the instructions on the label for safe handling and storage of this chemical.

Never-mix rules (memorize these)

These combinations produce toxic gas, fire, or violent reactions. Keep the items on separate shelves and never put them in the same bucket, drain, or spray bottle.

Item	Never mix with	Result
Bleach or calcium hypochlorite	Acids (vinegar, muriatic acid, toilet bowl cleaner)	Chlorine gas
Bleach or calcium hypochlorite	Ammonia or ammonia-based cleaners	Chloramine gas
Bleach or calcium hypochlorite	Oils, glycerin, or other organics	Fire or explosion risk
Lye (drain cleaner)	Aluminum (foil, pots, some containers)	Flammable hydrogen gas
Lye	Acids	Violent heat and gas

Additional practical rules:

Never store chemicals in food or drink containers.
Keep original labels; if a container is damaged, replace the label or the container.
Store away from heat, sunlight, children, and pets. Lock or childproof cabinets if you have young children.
Do not smoke or use open flames near flammable liquids or aerosols.
When cleaning spills, ventilate the area and use the product’s own instructions.

Storage notes that matter for preparedness

Liquid bleach loses strength over time (often months, not years). Rotate it. Calcium hypochlorite lasts longer when kept dry.
Do not store large quantities of concentrated oxidizers or acids if you do not have a clear, labeled plan for using and rotating them.
In a flood or hurricane, move household chemicals to higher ground if it is still safe to do so (same guidance as on the evacuation page).
After an event, follow local instructions for household hazardous waste disposal. Do not dump chemicals into storm drains or ditches.

Household chemicals worth stocking

A few plain products cover most cleaning and disinfecting needs after a storm. CDC says to clean with soap and water first, then sanitize or disinfect only if needed, and not to mix products or chemicals with each other. A product is an EPA-registered disinfectant only if its label carries an EPA Reg. No.; EPA verifies that registered disinfectants work according to their label directions.

Dish soap or detergent. The everyday cleaner. CDC says cleaning alone with soap or detergent removes most harmful viruses or bacteria from surfaces, and that surfaces should be cleaned before they are sanitized or disinfected. Ready.gov says to wash water-storage containers with dish soap before sanitizing them. CDC also lists dish detergent as an option for cleaning mold.

Unscented household bleach. This is what the site uses for drinking water (the EPA table above) and for sanitizing after a flood (CDC mixes). CDC says to use regular unscented bleach with 5%–9% sodium hypochlorite; some laundry and splashless bleaches are not appropriate for disinfection. A diluted bleach solution is not as effective after it has been mixed with water for over 24 hours, so make a fresh one each day. CDC says never to mix bleach with any other cleaner or disinfectant.

White vinegar. Useful in the pantry: the National Center for Home Food Preservation recommends white distilled or cider vinegar of 5% acidity for pickling, and says not to use vinegar of unknown acidity. What it is not: vinegar is not an EPA-registered disinfectant. EPA does not review how well household ingredients like vinegar or rubbing alcohol kill germs, so it cannot verify them. Never mix vinegar with bleach; the New Jersey Department of Health warns that the mix gives off chlorine and chloramine vapors (see the never-mix table above).

Hydrogen peroxide. Use it only as its label directs, and treat it as a disinfectant only if the label carries an EPA Reg. No. and disinfection directions. Never mix peroxide and vinegar in the same container: the New Jersey Department of Health says together they form peracetic acid, which can irritate the eyes, skin, and lungs. Do not mix it with bleach either (CDC).

Rubbing alcohol. EPA does not review how well it kills germs, so for disinfecting surfaces, keep an EPA-registered product as well. Never mix rubbing alcohol with bleach: the New Jersey Department of Health says the mix forms chloroform, which can cause dizziness, nausea, headaches, and loss of consciousness.

Baking soda. CPSC says to put out food fires with baking soda and never to use water or flour on cooking fires. It is not the tool for a grease or oil fire in a pan: CPSC says to slide a lid over the flames, turn off the heat, and leave the lid on until the pan cools. Call the fire department, and keep a fire extinguisher in the kitchen.

Mold cleanup after a flood

Dry fast. EPA says to dry water-damaged areas and items within 24–48 hours to prevent mold growth. If your home flooded and could not be dried within 24–48 hours, EPA’s disaster guide says to assume you have mold, and to throw away anything that was wet with floodwater and cannot be cleaned and dried completely within that window.
Size it up. If the moldy area is less than about 10 square feet (roughly a 3-foot by 3-foot patch), EPA says that in most cases you can handle the job yourself. For more than 10 square feet, or a lot of water damage, EPA points to its professional remediation guidance; if you hire a contractor, make sure they have mold cleanup experience.
Who should stay out. CDC says people with allergies, immune suppression, underlying lung disease, asthma, or COPD should not take part in mold cleanup.
What to wear. CDC: at least a NIOSH Approved N95 respirator; protective gloves (non-latex, vinyl, nitrile, or rubber); and goggles without open vent holes. Do not touch mold or moldy items with bare hands.
How to clean. EPA says to scrub mold off hard surfaces with detergent and water and dry them completely, and not to paint or caulk over mold.
Bleach is not required. EPA does not recommend bleach or other biocides as a routine part of mold cleanup, and notes that dead mold can still cause allergic reactions, so it must be removed, not just killed. CDC says bleach or dish detergent can be used; if you use bleach, use no more than 1 cup in 1 gallon of water, open windows or doors, and never mix bleach with ammonia or any other cleanser. The CDC flood-cleanup mixes are on the sanitation page.

Fuel and propane storage

Generator fueling and the 20-foot rule are covered on Power and lighting. For storage:

Gasoline. CPSC says to buy a child-resistant gas can, keep it capped, store it only in a well-ventilated, cool area, and never store gas cans inside a house, in a basement, or near pilot lights, stoves, heaters, or other ignition sources. Never use plastic bags or other makeshift containers. NFPA says to keep generator fuel in a container intended and labeled for it, outside living areas. USFA advises storing gasoline, oil, paints, and propane in a shed away from the house.
How much. Keep only what you can store safely, in the amounts your local fire code allows. Ask your local fire department if you are unsure.
Stabilizer and rotation. The Maine Department of Environmental Protection advises buying only what you need and not storing gasoline for more than 30 days unless a fuel stabilizer has been added, and choosing a stabilizer labeled for ethanol-blended gasoline if your fuel contains ethanol. Follow the stabilizer label for the dose. To rotate leftover fuel, the same page says unmixed old gasoline can be burned in a car by diluting one part old fuel with five parts new fuel.
Propane cylinders. CPSC says to always keep containers upright, never store a spare cylinder under or near the grill or indoors, transport it secured and upright, and never leave a filled cylinder in a hot car or trunk.
Kerosene. CPSC says to use only water-clear 1-K kerosene in a kerosene heater, never gasoline; store kerosene in a separate blue container meant for kerosene, never a red gasoline can; keep it away from other fuel containers; and never refuel a heater while it is running or hot.

Carbon monoxide

The full generator and carbon monoxide (CO) rules are on Power and lighting. The essentials, from CPSC:

Run portable generators outdoors only, at least 20 feet from homes and buildings, with the exhaust pointed away from windows, doors, and vents. Never in a house, garage, basement, crawl space, or shed, even with doors or windows open.
Never burn charcoal indoors or in a garage. CPSC also says never to use portable camping equipment such as camp stoves inside a home, garage, vehicle, or tent unless it is designed for indoor use, and never to use a gas range or oven to heat the house.
Install battery-operated CO alarms, or alarms with battery backup, on every level and outside sleeping areas, and test them monthly.
Early symptoms are like the flu without a fever: headache, fatigue, shortness of breath, nausea, and dizziness. Higher exposure brings confusion, vomiting, loss of coordination, and loss of consciousness (CPSC).
If a CO alarm sounds or anyone has symptoms, get everyone outside to fresh air immediately, then call 911. Do not go back in until responders say it is safe.

Mosquitoes after storms

CDC expects large numbers of floodwater mosquitoes in the weeks after flooding. Most are nuisance biters, but the kinds that can spread viruses may increase about two weeks after a hurricane.

Repellent. CDC recommends EPA-registered repellents with DEET, picaridin, IR3535, oil of lemon eucalyptus (OLE), para-menthane-diol (PMD), or 2-undecanone. Look for an EPA Reg. No. on the label; EPA’s repellent search tool helps you choose one.
Use it safely. Follow the label and reapply as directed. Do not put repellent on skin under clothing. If you use sunscreen, apply it first and repellent second. Do not use OLE or PMD products on children under 3. Do not apply repellent to a child’s hands, eyes, mouth, cuts, or irritated skin; adults should spray their own hands and then apply it to a child’s face. Permethrin is for clothing and gear, never skin (CDC).
Dump standing water. Once a week, empty and scrub, turn over, cover, or throw out anything that holds water: tires, tarps, buckets, toys, pools, birdbaths, flowerpot saucers, and trash cans. Use window and door screens, and do not prop doors open (CDC).
County mosquito control. Charleston County Mosquito Control: (843) 202-7880 or the request form on its mosquito control page. Dorchester County Mosquito Control: (843) 832-0080 or the online spray request on its mosquito control page. Berkeley County Mosquito Abatement: (843) 719-4646 during office hours, per its mosquito abatement page.

Household hazardous waste disposal

Do not pour chemicals, fuel, or oil down drains, into storm drains, or on the ground. Each county handles leftovers differently:

Charleston County. County residents can drop off household hazardous waste at the staffed convenience centers: household cleaners (including bleach, ammonia, and drain openers), paints and solvents, pesticides and repellents, used motor oil, and batteries. Old gasoline is accepted only at the Bees Ferry Convenience Center (gasoline only, no gas/oil mix). Locations, hours, and the full list are on the county’s household hazardous waste page; questions to Environmental Management at (843) 720-7111.
Dorchester County. The county’s convenience-site list includes antifreeze, lead-acid and rechargeable batteries, used motor oil and filters, used cooking oil, and old gasoline or oil/gas mixtures (Hwy 61 and Knightsville sites only). It does not list paint, pesticides, or household cleaners. Ask the Solid Waste Division at (843) 832-0070 about anything not on the list.
Berkeley County. Berkeley County Water & Sanitation’s convenience centers accept mixed oil and gas, cooking oil, antifreeze, used motor oil, and lead-acid and nickel-cadmium batteries. Its recycling page says the county has no paint recycling program: donate unused paint, or harden it with something like kitty litter or mortar mix before putting it in the trash, because the landfill cannot accept liquids. Damaged, defective, or recalled lithium-ion batteries go by appointment to the Oakley Road Convenience Center; call the Solid Waste Department at (843) 719-2383 or (843) 719-2386 (Berkeley County).

What this page does not cover

Treatment of water known or suspected to contain fuel, industrial chemicals, or radioactive material.
Stocking or using lye, strong acids, or other compounds for soap-making, food preservation, or other advanced uses.
Response to a major chemical release from a facility or transportation accident. For those, follow local emergency alerts and the guidance of the Charleston County, Berkeley County, or Dorchester County Local Emergency Planning Committee (LEPC).

Sources & further reading

On this site

Local water utility boil-water advisory contacts for Charleston, Dorchester, and Berkeley County utilities