A tricky pronoun

The text below is from an article titled as follows, "Roman Empire collapsed because they neglected environment."

In the article, the underlined 'them' seems to represent 'water.'
But how singular noun 'water' can be plural 'them'?

Or am I wrong in my idea of the pronoun 'them'?

The cleared soil was rich in minerals and nutrients and, at first, provided significant production yields. Unfortunately, the denudation of forest cover left the soil exposed to the elements. Wind blew across the barren landscapes, and water ran down from the mountaintops and slopes, taking the soil with them. Over-grazing of livestock resulted in further deterioration of the soil.