Weight of Water per Inch for Ponding Water
The following table provides the weight of water per inch in pounds for various areas/square footages. This should allow you to quickly and accurately estimate the weight of any amount of standing water on your low slope roof. One cubic inch of water weighs 0.036127 of a pound. One square foot of water one inch deep weighs 144 times this, or 5.202288 pounds. Everything else has been calculated from that.
This table should give you an idea of how much of a live load is being added to your roof by areas of ponding water or clogged drains.
Also see Roof Online’s Roof Drainage page.
Values for areas or depths not covered in the table should be easy to arrive at simply by adding together values for areas or depths which are listed.