Drainage
Why does water stand in one spot on my parking lot?
Water stands where the surface has settled below the grade around it, which means the base under that spot moved or a drain near it stopped working.
The numbers
- A lot is built with slope. Standing water means the slope is gone in that spot.
- Ponding softens the base under it, so the low spot keeps getting lower.
- Water standing near a grate usually points at the catch basin rather than the asphalt.
- Standing water is also where ice forms first every winter.
Why a lot is graded in the first place
Every lot is graded to move water to a drain or off an edge. When a spot holds water, something has moved. Either the ground under it has settled, which happens over an old utility trench or where the base was never compacted properly, or a catch basin has sunk and pulled the surface down with it.
Either way the water is now sitting on the one part of the lot least able to take it, which is the definition of a problem that grows.
What standing water does next
It soaks in. A saturated base loses strength, so the asphalt over it bends further under every vehicle, which cracks it, which lets more water in. In northwestern Wisconsin that water then freezes and lifts the surface, and the spring thaw leaves the area softer than it was the year before.
A puddle that has been there two seasons is usually alligator cracked by the third.
How the fix gets chosen
The first question is whether the drain is doing its job. A sunken or blocked catch basin has to be dealt with before any surface work, because a repaired surface draining into a failed structure sinks again.
If the drainage is sound and the asphalt has simply settled, the low area gets cut out and rebuilt back to grade. Filling a birdbath with sealer or a skim of material does not restore the slope and it does not stay.
Which of the two you have is not something to decide from a photograph. Walk the lot with somebody while the water is still standing, because the puddle is the evidence and it is gone by the afternoon.