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There is an unusual accumulation of rain water between my townhouse and my neighbor’s townhouse. I have checked and confirmed that the standing water comes from the roof gutter leakage during raining. Sometimes it takes more than 2 days for the water to go away after rain. I am not sure if there is any French drain system underneath the ground between our townhouses.

My neighbor said after putting gravel it helps the water go to the sewer system. I think that’s correct only if there is French drain system underground.

I am a bit concerned the standing water can have a long term effect on the corner of the foundation. Is my concern legit? Am I over thinking?

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    If water sits, then grading needs fixing. You want 1/4 to 1/2 inch slope per foot for water to drain away from foundations.
    – crip659
    Commented Jul 26 at 22:28
  • Well, it will certainly rot that wooden door. 1/8" per foot is the minimum grade generally recommended, and water does not flow uphill, though some terrible excuses for architects, landscape designers and occasionally even engineers have been known to draw plans claiming that it will.
    – Ecnerwal
    Commented Jul 26 at 22:37
  • The problem with gravel alone is it will quickly foul with silt and become ineffective.
    – Harper - Reinstate Monica
    Commented Jul 27 at 1:33
  • We need to know more. Got more pics with more context?
    – Huesmann
    Commented Jul 27 at 12:30

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You (and your neighbor) need to address surface drainage, which generally means lowering the area that is damming this water in between your houses.

If you'd also like to address sub-surface drainage, you can certainly do that, but that's a minor factor when you have surface ponding like this, which indicates that there is a barrier preventing the water from simply flowing away downhill, which is what the vast majority of the water should be doing on a properly landscaped yard.

No part of the yard adjacent to the house should be sloping towards the house. Nor should it be flat. It should slope away from the house by at least 1% grade, or 1/8" per foot (near enough at 1:96) or 1cm per meter (which is exactly 1%) A bit more is fine, particularly if there's lots of water. Less is not fine, and it must continue downhill until there's a suitable place for the water to collect without causing problems for the house.

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