When we eat plants we are eating lots of water. Consider a fresh apricot compared with a dried apricot.

The dried apricot is chewy and wrinkled because much of the water has been removed during the dehydration process. That water was turned to water vapour and went into the air.

If you eat a lot of watermelon you may need to pee more. Because there was a lot of water in it.

I forgot to water a plant of mine. The leaves went crispy and the whole pant shriveled up. Not only did it not get any new water to the point that it died… some of the water which was in the leaves and body of the plant was lost and is no longer in the plant anymore.

Dried herbs are dryer than fresh herbs. Because some of the water that was in the plant is no longer in the plant. It went somewhere else (likely into the air as water vapour).

Of course some of the water was used to build the plant itself as it didn’t come from nowhere.

The plant uses water and carbon dioxide to build sugars.

When you breathe in your breathe in oxygen (plus other gassed) When you breathe out you breathe out carbon dioxide (plus other gasses).

Where does the carbon come from? From the plants you eat.

The sugars in the plant are turned back into water and carbon dioxide.