The confusion here comes from assumptions that are perhaps implicit in the statement, but not explicitly spelled out. We need to break down exactly what is meant by I need water. What is missing here is why you need water. The complete statement here is obviously, "I need water to live". Or even more precisely, "I need x liters of water every t seconds to live". Now that we've explicitly spelled out what we're saying, we can reason about it properly.

"If I need (and have always needed) x liters of water every t seconds to live, and I've been alive for more than t seconds, then at least x liters of water must have existed at some point in the past" is valid. It is also likely, based on what we empirically know about how water works, that at least that much water still exists, but that doesn't necessarily follow logically. Even then, we can easily construct a situation where it doesn't follow, especially if we change "water" to "water I can access": just place me in a space capsule with only a finite amount of water, and at some point, toss it out the airlock. I still need accessible water to live, but there isn't any left.

What is valid empirical reasoning is, "If I am thirsty, and cease to be thirsty when I drink water, then not only does water exist now, but it probably also existed when humans first evolved." But the fact that we need it in the present doesn't imply that it will always exist in the future. There have been many situations where a species needs something to live, and that thing ceases to exist (at least in sufficient quantities). The result of such situations isn't contradiction, but rather extinction. And during the last moments before extinction, the species still exists, but the necessary resource does not.

The confusion here comes from assumptions that are perhaps implicit in the statement, but not explicitly spelled out. We need to break down exactly what is meant by I need water. What is missing here is why you need water. The complete statement here is obviously, "I need water to live". Or even more precisely, "I need x liters of water every t seconds to live". Now that we've explicitly spelled out what we're saying, we can reason about it properly.

"If I need (and have always needed) x liters of water every t seconds to live, and I've been alive for more than t seconds, then at least x liters of water must have existed at some point in the past" is valid. It is also likely, based on what we empirically know about how water works, that at least that much water still exists, but that doesn't necessarily follow logically. Even then, we can easily construct a situation where it doesn't follow, especially if we change "water" to "water I can access": just place me in a space capsule with only a finite amount of water, and at some point, toss it out the airlock. I still need accessible water to live, but there isn't any left.

What is valid empirical reasoning is, "If I am thirsty, and cease to be thirsty when I drink water, then not only does water exist now, but it probably also existed when humans first evolved." But the fact that we need it in the present doesn't imply that it will always exist in the future. There have been many situations where a species needs something to live, and that thing ceases to exist (at least in sufficient quantities). The result of such situations isn't contradiction, but rather extinction. And during the last moments before extinction, the species and the need still exist, but the necessary resource does not.