As a concept, vertical farming has been around for decades, and thinkers like Columbia professor Dickson Despommier are credited with advancing the concept. Until recently, however, it was never economically viable.Even now, the concept has major drawbacks. It's capital-intensive to start a vertical farm, energy costs can run very high, and space constraints limit what can be grown. Due to the lack of soil, the produce also doesn't get an organic label—even though it costs consumers about as much as organic products do.

"The challenge has been to make it commercially profitable," said Colangelo. "We looked at a number of different methods and through trial and error we figured out how not to build a farm." Recycling, filtering and sterilization system is the additional merit  with the goal of recycling 98% of the water used.All fresh water into Vertical Farm System installations has particulate, fluoride and heavy metal contaminants removed and is sterilised before entering the system.City wastewater(mainly gray water, which is water coming from households with the exception of that coming from toilets) can be treated to use in such vertical farms and this could lead to much lower costs for an urban area as such treatment can be done within the city and the water supplied to the vertical farms.

Dear Petr Kirpeit,

Please find the link for more information to support your question.

http://onlinelibrary.wiley.com/doi/10.1002/fes3.83/pdf

http://www.bbc.com/future/story/20170405-how-vertical-farming-reinvents-agriculture

http://www.basicknowledge101.com/subjects/verticalfarming.html

Thanks!

@Wajid Nasim Jatoi 

Its interesting, but Im looking for clear prepared data.

To see how many sqm salads consumes water per day, etc.

Something like this what allow to calculate the values.

For hydroponic systems, we need 5 to 7 liters of water per square meter per day for producing leafy vegetables.