Here�s an example of an extremely efficient hydroponic lettuce production facility in Mirabel, Quebec.  It covers many acres, growing lettuce on floating styrofoam rafts on shallow water tanks year round, yielding 5 times the amount per square meter as soil-based seasonal agriculture can produce.  Moreover, because the water tanks are completely covered, the only water lost is that due to evapotranspiration by the plants.  The water has been recycled for years.  This facility, too, is computer controlled, the water quality is constantly monitored and virtually no chemicals are used for pest and pathogen control.