The water column indicates the pressure at which a material lets water pass through it. To test the waterproofness of a textile, a so-called hydrostatic pressure test is performed. A cylinder is placed on the gazebo textile and is then gradually filled with water. The water pressure starts at zero and then increases by 10 mm per second. The test stops as soon as the third drop penetrates the textile and is visible on the inside.
Calculation example: if, after 10 minutes, the textile lets through exactly three drops of water, i.e., 1000 mm, the test is over and the textile has a water column value of 1000 mm.
As a rule of thumb, consider that: the higher the water column, the more waterproof the textile.