Water has a density that is 13.6 times less than that of mercury. how high would a column of water need to be to measure a pressure of 1 atm?

The density of mercury is 13560 kg/m³.
Therefore the density of water is about 1000 kg/m³.
1 atm pressure is 101325 Pa.
g = 9.8 m/s²

The height of a water column, h, needed to measure 1 atm is given by
(1000 kg/m³)*(9.8 m/s²)*(h m) = 101325 Pa
h = 1013225/9800 = 10.3393 m = 1033.93 cm

10.339 m or  1033.9 cm