I've often found myself pointing this out to people when talking about water being used, though it does depend a lot on where the water comes from, and / or being diverted away from.
I'm sure there is room for improvement in the methodology. There almost always is. You can contact the first author here [1] and I am sure, as a scientist, she would appreciate your correspondence.
[1]: https://www.dtu.dk/english/service/phonebook/person?id=80447
Paper is a particularly bad replacement as it falls apart when wet - a couple of days ago a paper bag did this to me as I walked back in light rain. Additionally, paper necessarily has a higher environmental cost due to the weight and packing fraction of the raw materials.
I shared that number because it shocked me and the report looked authoritative. Thanks for helping to add context to it :)