Does human organism consume water or is it only used as solvent?
Humans and all other animals actually are net producers of water ("metabolic water") by oxidizing sources of energy including fats, proteins, and carbohydrates - effectively the opposite of the chemical reactions that photosynthetic plants use to turn water and atmospheric CO$_2$ into biological materials and oxygen gas. There are also many metabolic reactions in humans that consume water (in particular hydrolysis reactions), but it is less than the amount produced.

However, water is indeed important as a solvent, and there are non-negligible losses through evaporation (especially when sweating) and an important role of water in the kidneys to assist in flushing waste.

If one was able to reclaim all evaporative losses and excretion losses, no additional water would be necessary. However, the energy requirements to do so go up exponentially the closer you get to 100% reclaimation.

The International Space Station has several water recovery systems to reduce the incredibly expensive cost of supplying enough water for humans on long missions in space. These systems include both urine purification and atmospheric reclamation but they do not approach 100% capture.