Where does the water hide on a rowhouse lot?
Start below grade. The basement areaway is the classic District breeding site: a small sunken space that collects leaves and grit, drains through one grate, and holds several inches of shaded water once that grate clogs. Nobody sees it from inside, and it can run all summer. Go up next. Flat and low slope roofs are common in Washington, and their drains and scuppers back up when debris collects. A shallow puddle on a roof is invisible from the street and perfectly protected from disturbance. Then the alley. Catch basins, dumpster wells, and abandoned containers behind a block hold water that belongs to nobody in particular, which is exactly why it sits. After that, the deliberate water: planter reservoirs on a deck, a rain barrel, a stone basin, an umbrella stand that fills. And finally the gutters, which under mature street trees fill with leaves faster than most owners expect. That list takes half an hour to walk on a typical parcel, and on most properties three or four of those items account for the entire problem.
Why the season here is shorter than it feels
The calendar is more forgiving in the District of Columbia than the humidity makes it seem. March and April are preparation months. Clear the areaway grate, get the roof drains cleared, empty and store anything that filled over winter. Nothing is biting, so this costs no outdoor time. May is when the first generations appear and when larval control earns the most. Because winter lows near 28F end adult activity each year, the summer population is built from the spring rebound, and pushing that down early keeps the whole season lower. June through August is the routine: check the areaway after storms, scrub containers weekly, keep larvicide on schedule. This is also when residual treatment on shaded brick and planting is most useful. Late August into early September is the CDC's national West Nile peak, and it is the stretch to be consistent about repellent and screens. October tapers off, and by November biting is essentially done. Use the cold months to fix drainage, because water that sits in December is a breeding site waiting for May.
A block problem, not a yard problem
The single most useful number for someone living on an attached block is Culex flight range: up to two miles. That is enough to cover most of a quadrant. What follows from it is uncomfortable. You can empty every container on your property, keep the areaway spotless, and still get bitten every evening, because the insects hatched in a catch basin four streets over. The way to tell is timing. If biting drops for a few days after a barrier treatment and returns quickly, production is happening somewhere you are not treating. If your own water was the source, the improvement builds over two or three weeks instead of fading. When the source is off site, the effective moves change. Report standing water in an alley or public drain to the health department. Talk to the neighbors whose areaway or roof might be contributing, since that conversation costs nothing. And shift your own money from repeated spraying toward screens, a patio fan, and repellent, which protect you regardless of where the mosquitoes were born.
What should the first visit look like?
On a small parcel, a good first appointment is short and specific. Expect the provider to go into the areaway, not glance at it. Expect them to ask about roof access. Expect them to open the planter reservoirs on a deck rather than looking at them from the doorway. They should ask when you get bitten and where you are standing, because dusk biting in a Culex area points at standing water and shaded resting sites, and that shapes the entire plan. They should also ask about the alley, and ideally walk it. What you want afterward is written scope: which water gets larvicide and at what interval, which surfaces get residual product, how many visits the price includes, which months the schedule runs, and what is excluded. Roof drain clearing, gutter work, and screen repair usually fall outside a standard quote even though they are often the actual fix. If a proposal names a monthly price without naming a single breeding site on your property, there is nothing there to compare against another quote.
Renters, condo boards, and shared responsibility
Split it by what is part of the building. Roof drains, scuppers, gutters, the areaway and its drain, grading, and any installed water feature are owner or association items. Containers on a patio or deck, planters, and a birdbath belong to whoever brought them. In attached housing, more of the list than usual sits on the building side, which is why an individual unit often cannot solve its own mosquito problem. If you rent, clear your own containers first so the remaining issue is clearly structural, then send the roof and areaway items in an email with photos and dates. Those requests are cheap and easy to approve. If you are on a condo board or manage a building, one spring pass on roof drains and areaway grates prevents most of the complaints that arrive in July, and it costs less than repeat service visits across a summer. Where several units share a courtyard or garden, treat the space as one property. Treating half of a shared area and skipping the rest reliably disappoints everyone involved.
How do you compare two mosquito quotes?
Compare what is being done before comparing what it costs. Ask what water they found. On a compact urban lot, a provider who inspected properly can name the areaway, the roof scupper, or the planter reservoirs without prompting. Ask whether larvicide is included and where it goes. Water in a sump or an areaway needs treating on its own three to four week interval, separate from anything sprayed on surfaces. Ask which surfaces get residual and how much area that covers. On a small parcel this can vary widely between quotes without either one saying so. Ask which months the plan runs. Activity here spans roughly May through October, so a plan of four summer visits leaves both ends open. Ask what is excluded, and expect roof work, gutter clearing, and screen repair to be on that list. Finally, ask what happens if biting has not eased after two visits. A provider who has a real answer to that question, usually involving re inspection rather than more product, is the one worth hiring.