A flooded basement is one of the most common and costly home disasters. Most flooding is preventable by managing where water goes before it reaches the foundation, plus a couple of devices for when it does.
Manage surface water
Grade the soil to slope away from the house, extend downspouts well away from the foundation, and keep gutters clear so they don't overflow against the walls. These cheap steps stop most water-entry problems.
Sump pump and backup
If your basement relies on a sump pump, test it regularly and add a battery backup so it keeps working during the storm-driven power outages when you need it most.
Backwater valve
In areas prone to sewer backup during heavy rain, a backwater valve on the main drain prevents sewage from flowing back into the basement. Some municipalities offer rebates for installing one.
Maintain drainage
Keep weeping tile and yard drains clear, and address any chronic wet spots early. Standing water near the house is a warning sign worth acting on before the next big storm.