If the municipal sewer main under your street backs up and fills your finished basement with three inches of sewage, your homeowners policy pays nothing. Neither does a flood policy, if you have one. Both exclude it in almost identical language, which is a strange thing for two policies to have in common, and it leaves exactly one product standing: a water backup coverage endorsement that most carriers sell for somewhere between $55 and $175 a year.
The articles that rank for this all tell you to buy it. None of them tells you that the limit they are selling you is wrong.
Water backup coverage exists because two other policies exclude it
Start with the standard homeowners form, because the wording matters. The ISO HO-3 Special Form, the basis for most policies sold in America, excludes loss caused by water that “backs up through sewers or drains” or that “overflows or is otherwise discharged from a sump, sump pump or related equipment.” That sits inside an exclusion applying “regardless of any other cause or event contributing concurrently or in any sequence to the loss,” so you cannot argue around it by pointing to something covered that also contributed.
Now the confusing part, and the reason people think they are covered. The same policy does cover accidental discharge of water from within a plumbing system or a household appliance. A burst supply line, a failed dishwasher hose, a tub overflowing because of a clog inside your own pipes: all covered. The form even carves back the surface water and groundwater exclusions for those losses. What it deliberately does not carve back is the sewer and sump clause, and it expressly writes the sump out of the definition of a plumbing system.
Courts have drawn the line at the property line. The clearest statement comes from a Washington appeals case, Hallsted, in 1979: if the blockage is inside your system, like a clogged sink drain, the exclusion does not apply. If the cause sits outside it, like a clogged sewer pipe forcing water back into the house, the exclusion applies even though the water arrived through your own pipes. A Florida court put it more bluntly in 1992: a sewer or drain begins at the property line.
So the same puddle is covered or not depending on which direction the water was traveling and where the obstruction sat.
And flood insurance does not fill the hole. The Standard Flood Insurance Policy in 44 CFR Part 61 excludes water that backs up through sewers or drains, or discharges from a sump, “unless there is a flood in the area and the flood is the proximate cause.” A flood, under the same regulation, means inundation of two or more acres or of two or more properties. A blocked main on your street that floods your basement alone qualifies as neither. A homeowner who bought a full HO-3 and a full flood policy and skipped the $75 endorsement has zero coverage for the single most likely basement loss.
What it costs, and what the limits look like
Carriers do not publish this on their consumer pages. Amica, American Family, Liberty Mutual and Nationwide all describe the coverage without naming a dollar limit anywhere, which is its own tell. The hard numbers live in filed rate manuals.
Auto Club’s homeowners rules manual for Indiana, form CO 04 95, lays out the ladder plainly: $5,000 of coverage for $75 a year, $10,000 for $125, $20,000 for $175. Those rates carry a 2011 effective date, so read them as the shape of the pricing rather than today’s quote. The Hanover publishes a broader range on its own site, $50 to $250 a year, for limits running from $5,000 up to the full replacement cost of the home.
The base ISO endorsement, HO 04 95, carries a flat $5,000 limit and a $250 deductible with the notable instruction that “no other deductibles apply.” A newer form goes up to the full policy limit. Which one you get depends heavily on your state: Maryland and North Carolina variants provide up to the policy limit, while New York, Pennsylvania, Texas, Vermont, Oregon, Alaska and Florida variants cap at $5,000.
Watch the deductible, because it moves in both directions. The ISO form’s $250 replaces your policy deductible, which is better than your main deductible for most people. Auto Club’s Indiana rule does the opposite: “$500 deductible or the policy deductible, whichever is greater.” Ask which applies before you assume anything.
Why $5,000 does not cover it
Here is the arithmetic the ranking articles never run.
Take a 1,000 square foot finished basement and sewage rather than clean water. Contractor cost data compiled in February 2026 puts water extraction, drying and sanitizing at $4 to $12 per square foot before any rebuilding begins, so $4,000 to $12,000 on that footprint. Class 3 damage, the extensive category, runs $5,000 to $8,000 to repair. Mold remediation, which starts becoming necessary within 24 to 48 hours, adds $1,500 to $6,000. A furnace sitting on that floor costs $3,500 to $7,500 to replace and a tank water heater $600 to $3,100.
Add the low end of each: roughly $18,000. Add the middle: closer to $30,000.
Against that, a $5,000 sublimit covers somewhere between a quarter and a third of the extraction step alone, before a single sheet of drywall goes back up. And in Auto Club’s Indiana filing, moving from $5,000 to $20,000 of coverage cost an extra $100 a year. Ten years of that upgrade runs about $1,000 against $15,000 of additional recovery. That is the trade, and it is not close.
Sewage makes it worse in a way volume alone does not explain. Category 3 water requires removal of all porous material regardless of how fast you respond, so carpet, pad, drywall and insulation come out whether or not you had a fan running within the hour. You cannot dry your way out of a sewage loss the way you can a clean water loss.
One thing the endorsement will not do: replace the sump pump itself. Every version excludes direct physical loss to the equipment, and a new pump runs $600 to $2,500. The endorsement covers what the failure did to your house, not the thing that failed.
Do not count on the city
People assume the municipality pays when the municipal main is the problem. Metro Detroit settled that question at scale.
After the storms of June 25 and 26, 2021, the Great Lakes Water Authority received basement flooding claims from more than 24,000 water and sewer customers, with roughly 23,000 more going to Detroit’s own water department. In July 2022 the Authority denied all of them, relying on an engineering report concluding the cause was historic rainfall exceeding the system’s design capacity rather than any defect in the collection system. Michigan’s governmental immunity statute requires a formal notice of claim and permits recovery only through a narrow sewage disposal event exception, so most homeowners who waited for the city recovered nothing.
The infrastructure trend is not encouraging either. The American Society of Civil Engineers graded the nation’s wastewater systems D+ in its 2025 report card, noting that collection system failures rose from 2 to 3.3 per 100 miles of pipe, that the renewal rate for large capital projects fell from 3% to 2% over the decade, and that 738 combined sewer systems are still in operation. Annual capital need runs about $99 billion against roughly $69 billion of funding.
One myth worth correcting
You will read that a single water claim wrecks your renewal through your CLUE report. That is half wrong, and the correction comes from a regulator. Wisconsin’s Office of the Commissioner of Insurance, in guidance revised in May 2026, says CLUE holds seven years of claim history but that “reports are used almost exclusively to underwrite and rate new policies. Most insurers renewing existing policies do not access C.L.U.E. reports at renewal,” because they already have your loss history.
So the claim does not blindside your current carrier, who already knows. It bites when you shop, switch or sell, and it follows the property for seven years. Worth knowing, but not a reason to eat a $20,000 loss rather than file.
What to do this week
Pull your declarations page and look for a line mentioning water backup, sewer backup, or sump overflow. If it is absent, you do not have it. If it is present, find the limit, and if that limit reads $5,000, call and ask what the next two tiers cost and which deductible applies to the endorsement. The upgrade is usually a rounding error on the annual premium.
Then spend an afternoon on the physical side, because water backup coverage pays for damage and does nothing to prevent it. A backwater valve on the sewer lateral, a battery backup on the sump pump, and nothing greasy or flushable-in-name-only going down the drain will do more for you than any endorsement limit. While you are auditing the policy, our guide to cutting your homeowners premium covers where to find the offsetting savings, and the flood insurance waiting period matters if you are also exposed to the kind of water that actually qualifies as a flood.
