H2O | Column [molecules/cm2 ] to column [mm] conversion

Greetings Sander,
A quick question: in the conversions I was trying to find if one can change the GOME2 H2O column into units that are typically used in describing precipitable water content, i.e. mm.
So far I’ve been checking http://stcorp.github.io/harp/doc/html/algorithms/index.html#variable-conversions
for possible conversions, is there another link I am missing?
Many thanks,

Water content is usually provided as a mass density (e.g. kg/m2). This includes all types of water content, including water vapour, ice water content, liquid water content, rain, and snow.

I assume you are talking about TPW? Even in that case a commonly used unit is still kg/m2.

I find the ‘column length’ variant a bit awkward. It is a virtual quantity (since you don’t actually have a column of water with that length). And this means that (as far as I can see it) it doesn’t really fit into the list variables for HARP (since you can’t really perform any sensible operations with that length value).