Every November I get at least one call that starts with "so, there's water in the basement." It's almost never the roof. It's a garden hose still screwed onto the outside spigot of a Lincoln Park greystone. Behind the brick, a pipe froze and split the first night the temperature dropped into the low 20s.
Here's how it happens. The spigot looks fine from outside. The crack is inside the wall, in the stretch of pipe that runs through the foundation. Nothing leaks while it's frozen. Then the afternoon warms up, the ice lets go, and water runs quietly into the finished lower level until somebody notices the carpet squishes. By then you're paying for drywall, flooring, maybe a mold crew. In a nicely built-out garden unit that's a five-figure bill for something a five-dollar part would have prevented.
The fix is boring, which is why nobody does it. Find the interior shutoff valve for each exterior line (it's usually in the basement ceiling near the front or back wall) and close it. Then open the outside spigot and let it drain. Take the hose off. If your building has frost-free sillcocks, the hose still has to come off, because a connected hose traps water in the exact part that's supposed to drain. Chicago's first hard freeze lands around late October most years, so do this weekend. Thanksgiving is too late.
Investors, this one's especially for you. I see it most in vacant units and in two-flats between tenants. Nobody's there to notice, the thermostat's turned down to save a few bucks, and the damage sits for weeks. Put the shutoff on your turnover checklist. Put it on your property manager's checklist too, and then actually check that it got done.
I've spent 20 years running real estate teams, and here's where I push back on a lot of agents. They love to call this a "minor maintenance item" in an inspection response. I don't. A buyer touring in December who smells a damp basement isn't going to negotiate over $500. They'll knock $25,000 off the offer, or they'll walk. The house barely changed. Their trust in it did.
Developers finishing new construction in Bucktown or the West Loop right now, label those interior valves before closing. Your buyer will thank you in February and won't even know why.