Did they even mention food and water in book 6? I just read it, not a week ago, and I don't recall them saying anything about feeding and watering Jake. It kind of skipped from the first night to the end of the third day, to my recollection.
It's an interesting question, though. And I remember in THBC, Esplin saying something along the lines of "We can make Kandrona starvation last for weeks" or something, and it would definitely be a painful death to keep nourishment from both host and Yeerk. However, I'd like to think the Yeerks are practical enough to want to protect hosts, since they're viable and important resources, but even keeping hosts healthy is a high cost. How exactly did Visser Three keep all of those Hork-Bajir and Taxxons fed? Taxxons eat each other, which seems impractical but it's an answer, and there was that water/air truck ship in book #3, but what about bark? Did they just unleash armies of Hork-Bajir into the National Park to strip as many trees as far away from civilization as possible?