I think that the loss of the water filter was the critical mishap.

Most modern filters will allow you to process a litre of water in about 1-5 mins. Depending on capacity. Assuming that its a filter and not a purifier you are still going to have to chemically treat the water with chlorine or iodine.

Let us assume that the water is cold so you need a contact time of about 30mins. Just to be certain.

Call it a maximum of 45mins per bottle of water.

That looks bad but normally you would be drinking one bottle whilst the rest are "fizzing."

Under those conditions you probably need at least 6litres per day. I reckon that he was getting no more than 2-3.

Dehydration impairs your ability to think clearly and to digest your food. Which impairs your bodys ability to generate body heat and blood sugars.

So it follows that even mild dehydration can - under some circumstances - be a killer.