What does 'it' refer to in this context?

Question

What does the following it(bold letter) refer to? Is this a Provisional subject? If you have any good idea, please let me know.

It is estimated that about one-third of the population in Sub-Saharan Africa must travel at least thirty minutes to the closest water source, often several times a day. This burden falls mainly on women and girls. As a result, many women cannot do any other work, and many young girls cannot attend school. Children are also usually the first to get sick or die from drinking dirty water. People in developed countries like Japan may feel that this problem does not relate to them, but this is not the case. Developed countries contribute to this problem in a major way through their use of virtual water. Virtual water refers to the total amount of water used to make and transport food and products like clothing and electronics. For example, when considering the amount of water it takes to raise, prepare, and transport beef, a single hamburger uses about 2,400 liters! Japan is the second largest virtual water importer in the world and, as such, shares responsibility for the Earth’s water crisis.

Answer 1

This looks like an "empty it" or "dummy it". See: this description of the concept. This "it" isn't referring to anything in specific, instead, it acts as a placeholder subject for the grammatical purpose of the subject when we don't need one.

One way to rephrase the sentence and keep the exact same meaning would be:

...when considering the amount of water required to raise, prepare, and transport beef...

Note how this rephrasing uses the passive voice, which also removes the subject.