Usually not for groundwater seepage or surface water, which standard policies exclude. Sudden internal failures like a burst pipe are typically covered, and sewer or drain backup requires a separate rider most policies do not include by default.
More detail
This is where a lot of homeowners find out what their policy does after the fact, so the categories are worth knowing before the water arrives. Generally excluded on a standard policy: water that enters from the ground or from the surface. Groundwater seepage through walls or the cove joint, surface water running toward the house, and flooding are all in this family. Flood specifically requires separate flood insurance, which is a different product entirely. Generally covered: sudden and accidental discharge from a system inside the house. A burst supply line, a failed water heater, or an overflowing appliance is the classic covered loss. The important middle: sewer and drain backup, and sump pump failure. These are typically excluded from the base policy and available as an endorsement, often for a modest annual premium with a coverage limit you choose. Many homeowners with sump pumps do not have it and assume they do. If your basement is finished, this is the rider worth confirming. What to do at the time of loss regardless of coverage: document before mitigating, as covered in the first-hour guidance, keep receipts for extraction and drying, and report promptly. Insurers can and do deny on late notice. What gets claims denied beyond the exclusions: a maintenance argument, meaning the insurer contends the condition was gradual and known rather than sudden. That is another reason the dated photographs of a first-time event matter, and a reason not to leave a known seepage problem undocumented and unaddressed for years. Worth a phone call to your agent before the next storm: ask specifically whether you have water backup coverage, what the limit is, and what the deductible is on it.