# CDC Standing Water Rule: Empty and Scrub Containers Once a Week

> Standing water mosquito control: the CDC says empty and scrub weekly, EPA says empty and change weekly, and the CDC names Bti for water you cannot dump.

Source: https://longsleeve.com/blog/standing-water-mosquito-control

By [Andrew Rothaus](https://longsleeve.com/about), Founder · August 6, 2026 · Updated September 13, 2026

Standing water is where mosquitoes are made. EPA calls egg and larva interventions generally the most effective, least costly way to control mosquitoes. The CDC's instruction is to empty and scrub, turn over, cover, or throw out anything holding water once a week, because an egg can reach adulthood in 7 days.

CDC and EPA home guidance is built almost entirely around containers. Water sitting in something on your property, or the one next door, is where the next generation gets built. Containers are the one stage of the life cycle a homeowner can reach.

## Why does standing water decide how many mosquitoes you get?

EPA lays out the life cycle in four stages: egg, larva, pupa, adult. The agency's summary is the whole argument in one line: "The first three stages occur in water, but the adult is an active flying insect." Three of those four stages happen in water you can tip over.

**Short answer:** Standing water is where mosquitoes are made. CDC guidance is to empty and scrub, turn over, cover, or throw out items that hold water once a week. That weekly cadence matters because the CDC says mosquito eggs can develop into adults in 7 to 10 days, and *Aedes* eggs can stick to container walls and survive drying out for months.

Then it moves fast. The CDC gives the same figure for both groups: a mosquito egg takes 7 to 10 days to develop into an adult. EPA's cross-species estimate is that "The life cycle typically takes up two weeks, but depending on conditions, it can range from 4 days to as long as a month."

## How little water does a mosquito actually need?

Less than you think. The CDC states it plainly: "Mosquitoes only need a small amount of water to lay eggs. Bowls, cups, fountains, tires, barrels, vases, and any other container storing water make a great 'nursery.'" EPA goes smaller still, listing [Aedes aegypti](https://longsleeve.com/blog/aedes-aegypti) sites as "old tires, buckets, toys, potted plant trays and saucers, plastic covers and even places as small as bottle caps," with a preference for "dark-colored containers located in the shade."

Dry does not mean clear, either. CDC says *Aedes* eggs "can survive drying out for up to 8 months" and "can even survive a winter in the southern United States." Floodwater species lay above the water line, and per the CDC "The eggs dry out, then hatch when rain floods the soil or container." An empty saucer that has sat dry for a month is still well inside that 8 month window.

## Which containers does the CDC actually name?

The CDC's home control page names these directly: "tires, buckets, planters, toys, pools, birdbaths, flowerpot saucers, or trash containers." Its larvicide guidance adds "Buckets and rain barrels," "Fountains," "Gutters or downspouts," "Non-chlorinated swimming pools," "Pool covers that collect water," "Tires," and tree holes.

Two categories are easy to miss. The CDC tells homeowners to "Fill tree holes" and to "Repair cracks or gaps in your septic tank if you have one. Cover open vent or plumbing pipes." It does not stop at the door: "Mosquitoes entering your house from outdoors can start laying eggs indoors," so the weekly routine applies to indoor items "such as vases or flowerpot saucers." For water you do not own, in "Neglected swimming pools," "Trash," "Discarded tires," or "Drainage ditches with standing water," the CDC says to call your local mosquito control board or health department.

## Why once a week, and why scrub?

The weekly interval sits at the fast end of the 7 to 10 day egg-to-adult window the CDC gives for both *Aedes* and *Culex*. That is why the CDC's instruction is weekly and not monthly.

The scrubbing is the part people skip, and it is the part that deals with eggs glued above the waterline. The CDC's instruction is to "empty and scrub, turn over, cover, or throw out any items that hold water," and the reason it gives is "to remove mosquito eggs and larvae." Tipping a birdbath removes the water. Scrubbing the sides removes the eggs.

For water you want to keep, the CDC says to "Tightly cover water storage containers (buckets, cisterns, rain barrels) so mosquitoes cannot get inside to lay eggs," and "For containers without lids, use wire mesh with holes smaller than an adult mosquito." EPA adds: "Keep swimming pool water treated and circulating."

## What does the EPA say about standing water?

Empty and change the water in the containers that hold it, at least once a week, and get rid of standing water everywhere else. That is EPA's own instruction, on its Tips to Prevent Mosquito Bites page: "Empty and change the water in bird baths, fountains, wading pools, rain barrels, and potted plant trays at least once a week to destroy potential mosquito habitats."

The rest of EPA's list overlaps the CDC's above: "Eliminate standing water in rain gutters, old tires, buckets, plastic covers, toys, or any other container where mosquitoes can breed," and "Drain or fill temporary pools of water with dirt." Old tires, buckets, plastic covers and toys are also on EPA's [Aedes aegypti](https://longsleeve.com/blog/aedes-aegypti) list higher up this page.

EPA's reason is eggs: "An important part of mosquito control around homes is making sure that mosquitoes don't have a place to lay their eggs." Its Bti page puts the same instruction at the smallest scale, "Eliminate any standing water (even tiny amounts)," to keep mosquitoes from laying eggs there.

Between the two agencies the calendar is the same, weekly, on anything that holds water; the scrub step is the CDC's wording. How many weeks that runs depends on your region, laid out in [when mosquito season starts and ends](https://longsleeve.com/blog/mosquito-season-by-region); if the water sits where you eat, see [keeping mosquitoes away from a patio dinner](https://longsleeve.com/blog/how-to-keep-mosquitoes-away-from-patio-dinner).

## What do you do with water you cannot dump?

That is what larvicides are for. The CDC's rule is narrow: use larvicides on standing water that "Will not be used for drinking" and "Cannot be covered, dumped, or removed," which its Bti fact sheet illustrates with "rain barrels, fountains, ornamental ponds, septic tanks, and pools that are not in use."

The CDC says "Homeowners can use mosquito dunks or bits that contain larvicide," applied by hand to small bodies of water. The larvicide the CDC lists first is Bti, *Bacillus thuringiensis* subspecies *israelensis*, a soil bacterium the CDC calls "toxic to mosquito larvae, blackflies, and fungus gnats" that "has been used for mosquito control for more than 30 years." One limit matters: the CDC states flatly that "Bti does not control biting female mosquitoes." It works on the nursery only.

EPA has registered five strains of Bti across 48 pesticide products. Its toxins "specifically affect the larvae of only mosquitoes, black flies and fungus gnats" and "do not affect other types of insects including honey bees." The National Pesticide Information Center adds that Bt "has to be eaten to work." On use, the CDC is direct: "Follow the instructions on the label. Do not apply more than directed or reapply more often than instructed."

## What container control cannot do

EPA is honest about the ceiling: "Egg and larva interventions are generally the most effective, least costly, way to control mosquitoes. However, these interventions are unlikely to be 100% effective, especially for mosquitoes like the *Aedes aegypti* that breed in varied and scattered locations." In those cases, EPA says, "eliminating or treating all or even most standing water can be nearly impossible."

So the CDC pairs water control with barriers and personal protection: "Use screens on windows and doors," "Use air conditioning, if available," and "Wear loose-fitting, long-sleeved shirts and pants." For repellents, the CDC says to "Use EPA-registered insect repellents" with one of six active ingredients it lists: DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol, and 2-undecanone. The CDC names active ingredients, not brands, and tells everyone to "Always follow the product label instructions."

## What does the evidence say about the devices people buy instead?

Start with the regulatory gap. Bug zappers, insect traps, and ultrasonic sound generators are classified by EPA as devices, not pesticides. Per EPA's consumer guide, "FIFRA does not require devices to undergo premarket review and registration," and manufacturers "do not submit their claims or efficacy and safety data to EPA (for approval or otherwise) before selling or distributing a device." On the number on the box, the agency is blunt: "An EPA establishment number on device packaging does NOT indicate that the product has been reviewed for safety or efficacy by EPA."

Then the field data. A 2007 Cochrane systematic review of electronic mosquito repellents, the ultrasonic units, found ten qualifying field studies. "All 10 studies found that there was no difference in the number of mosquitoes caught from the bare body parts of the human participants with or without an EMR." The authors' conclusion: "Field entomological studies confirm that EMRs have no effect on preventing mosquito bites."

Electric zappers have their own record. Frick and Tallamy, in Entomological News in 1996, counted every insect killed in six suburban traps over a season. Out of 13,789 insects there were "only 31 biting flies, a minute proportion (0.22%)," while the traps destroyed "1,868 predators and parasites (13.5%) and 6,670 nonbiting aquatic insects (48.4%)." Their verdict: "electric insect traps are worthless for biting fly reduction."

Wearables did not fare much better in a 2017 wind tunnel study in the Journal of Insect Science. Of five wearable devices tested against *Aedes aegypti*, "only the one that releases Metofluthrin significantly reduced the numbers of attracted mosquitoes. The [citronella candle](https://longsleeve.com/blog/citronella-and-plant-repellents) had no effect."

## Does your neighbor's bucket matter?

Enormously, and so does yours. The CDC notes that *Aedes aegypti* and *Ae. albopictus* "don't fly long distances" and that "In their lifetime, these mosquitoes will only fly a few blocks." *Culex* mosquitoes "don't fly long distances but have been known to fly up to 2 miles (3.2 km)." Either way the range is short, which is why EPA says "Residents, neighbors, and landlords can all be proactive in eliminating standing water or alerting others to its presence." If numbers in your area are high, the CDC says to call your local or state health department or mosquito control program.

If ticks are also on your list, we cover their calendar in [when tick season runs](https://longsleeve.com/blog/tick-season-when).

## Where Longsleeve fits

Longsleeve is an EPA-registered picaridin lotion (EPA Reg. No. 101457-1). It repels mosquitoes and ticks for up to 14 hours. It is fragrance-free, with nine disclosed ingredients, all listed on our [facts page](https://longsleeve.com/facts).

## Common questions

**How much standing water does it take to breed mosquitoes?**

Very little. The CDC says mosquitoes "only need a small amount of water to lay eggs," naming bowls, cups, tires, barrels, and vases. EPA's list of Aedes aegypti sites includes "even places as small as bottle caps."

**Why once a week instead of once a month?**

The CDC puts egg-to-adult development at 7 to 10 days for both Aedes and Culex mosquitoes, which is why its instruction is weekly rather than monthly.

**Is dumping the water enough, or do I need to scrub?**

The CDC's wording is "empty and scrub," and the stated purpose is "to remove mosquito eggs and larvae." Aedes females lay above the waterline, the eggs "stick to container walls like glue," and they "can survive drying out for up to 8 months."

**Do ultrasonic repellers or bug zappers reduce mosquito bites?**

The published evidence says no. A Cochrane review of ten field studies concluded that electronic mosquito repellents "have no effect on preventing mosquito bites." A 1996 Entomological News survey found biting flies were 0.22 percent of insects killed by suburban electric traps, and called them "worthless for biting fly reduction."

**What about a pond or rain barrel I cannot empty?**

The CDC says to use larvicides on standing water that will not be used for drinking and cannot be covered, dumped, or removed, naming rain barrels, ornamental ponds, septic tanks, and unused pools. Follow the label, and do not apply more or more often than directed. If you get sick after mosquito exposure, the CDC's advice is to talk to a healthcare provider.

**What can you put in standing water to stop mosquitoes?**

A larvicide. EPA's homeowner option is Bti, the soil bacterium described in the section above, and EPA says larvicides "target larvae in the breeding habitat before they can mature into adult mosquitoes and disperse." EPA says Bti "can be used around homes in areas and containers where water can collect, such as flower pots, tires, and bird baths," and "to treat larger bodies of water like ponds, lakes and irrigation ditches." Read the label: EPA says "some are allowed to be used on certain drinking water (e.g., cisterns) while others are not intended for that use," and the CDC's dunks-and-bits rules sit in the section above on water you cannot dump.

**Are mosquito dunks a risk to people or pets?**

EPA's statements are about Bti, the larvicide the CDC lists first for dunks and bits, not about any particular product. EPA says Bti "has no toxicity to people," that "EPA has concluded that Bti does not pose a risk to humans," and that "people do not need to leave areas being treated." For pets, the National Pesticide Information Center's Bt fact sheet says "pets and people might be exposed to Bt from treated birdbaths or water fountains," that you "can limit exposure and reduce risk by carefully following the label instructions," and that people and other mammals "do not have the specific enzymes that break down the spore proteins to release the toxins" and lack "the necessary receptors that insect guts have." NPIC's pointer is the label; for a pet that has been drinking from a treated birdbath, ask your veterinarian.

## Related reading

- [West Nile Virus in NYC, 2026](https://longsleeve.com/blog/west-nile-virus-nyc). The 2026 borough counts, the September spray schedule, and where 311 fits.
- [Aedes aegypti: The Yellow Fever Mosquito](https://longsleeve.com/blog/aedes-aegypti). The day-biting container breeder behind dengue and Zika.
- [When Is Mosquito Season?](https://longsleeve.com/blog/mosquito-season-by-region). Health-department months and temperature thresholds, region by region.
- [The Asian Tiger Mosquito](https://longsleeve.com/blog/asian-tiger-mosquito). A daytime biter that breeds in whatever holds water.
- [West Nile Virus in the United States](https://longsleeve.com/blog/west-nile-virus). The bird cycle, the late-summer peak, and who is actually at risk.
- [The almanac of biting insects](https://longsleeve.com/facts). The sourced field guide: species, ranges, and the diseases they carry.
- [Do Ultrasonic Repellers Work?](https://longsleeve.com/blog/ultrasonic-repellers). The gadget that keeps getting sold, and the evidence against it.

More Longsleeve in your Google feed:

## Sources

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Last reviewed 2026-08-06 · every claim on this page is sourced above

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