Five signs your basement is about to flood.

After thirty-four years and thousands of basements, I can tell you that almost no flood is a surprise. Houses give warning. The signs just look like ordinary weather to most homeowners. Here are the five we look for, in the order they tend to show up.

1. Efflorescence on the wall. That white powder that looks like chalk is mineral salts left behind by water moving through the foundation. It's not dangerous, but it tells you water is coming through somewhere — even if the basement still feels dry.

2. A musty smell that comes and goes with the weather. If you only notice the smell after a heavy rain or in early spring, that's water coming and going through cracks or the cold joint where the wall meets the floor.

3. Hairline cracks that you can see daylight through (or that get a little wider in the spring). A foundation that's settling or shifting will reveal itself this way long before water actually starts to come in.

4. The sump pump runs more often than it used to. A pump that used to cycle once a week and now runs every hour during a storm is a pump fighting a losing battle. Either the system around it is failing or the water table around your house has changed.

5. Water marks on stored boxes that you swear weren't there last year. People miss this one all the time. Cardboard against the wall picks up moisture you can't see on the wall itself. If your storage looks worse than it did last year, the wall is wet — even if it doesn't look it.

If any two of these are showing up at your house, it's worth a free estimate. Most fixes are a fraction of what a finished basement repair costs after a flood.