Why expect a powerful time machine to create mineral water. It is logical and more reasonable to expect a powerful mineral water machine to produce mineral water.
My vehicle, a Toyota Fortuner 3.0 engine is very powerful. We expect someone to ask us, "powerful for what?"
and not by "why can it not fly?"
Interestingly enough, the answer can be found using your own story about the diary.
You ask the question "what if, you and the guy existed in the same time frame...". I believe that is what will make the time machine powerful.
Please just don't expect mineral water. It is like asking God to be evil while having Him as the embodiment of goodness.