There's a photo of your future mold claim sitting on your phone. It's a drain full of dirt. Flooding shows up on a property, and the first call goes to the landscaper. He comes back with a proposal for a new trench and a couple of box drains. He is a reasonable guy who gives you a proposal that will fix the problem. What rarely happens first is somebody pulling that grate and cleaning out what's under it. Water is the most patient enemy a building has. It works nights and weekends. A one-inch-per-hour storm on a 10,000-square-foot roof throws about 104 gallons a minute at your site drainage. A clean 4-inch lateral at 1 percent slope carries about 100. You have no margin on a good day. Take away a third of that pipe with silt and leaves, and the water picks a new route. Usually through your slab. Dry day, here's what to look for: Puddles still standing 24 hours after the rain stopped Erosion behind the building, mulch fanned across the sidewalk, dirt washing out of the beds Rust streaks and dirt striping down the face of the gutter, which means it's been overflowing at the seams for years Alligator cracking and potholes clustered in one section of the lot. The base failed before the asphalt did Water sitting in the catch basin on a dry day. The basin is fine. The line downstream is plugged In the rain you don't have to look for anything. It shows you: A gutter waterfalling over the front lip while the downspout runs dry Water sheeting toward the building instead of away from it A grate with water pooled on top and no pull. Worse, water coming back up out of it The path residents take to walk around the puddle. They've been telling you for three years with their feet Then run the boring list. Find your outfall first, because that's where these systems die. A headwall that silted a year ago will back up a perfectly clean lateral. Then work backwards. Pull the grates and vacuum the basins out, landscaper or vac truck depending on the depth. Camera the lines. Confirm every downspout discharges 5 feet out. Shoot your grade. You want 6 inches of fall in the first 10 feet off the wall, and on a built-out site with sidewalks you often can't get it, which is exactly why the area drains are there. If you want to know how a property drains, walk it in the rain