Hydroponics is a technology for growing plants in nutrient solutions with or without the use of an artificial medium to provide mechanical support.
For nutrient solutions we understand water containing the appropriate salts and compounds. Plants rely in water and nutrients (that must be in their ionic form), for this reason, it is impossible to replace the water for the nutrient solutions representing a necessary payload to carry for an extended lunar mission and /or the first steps or the lunar colonization. Since it is possible to obtain water from lunar materials, the concern is to calculate what amount of this water is going to be destined for the hydroponic system.
See also: Plant nutrients
The most important dissolved ions needed are Ca2+, Mg2+, K+, NO3- (nitrate), SO42− (sulfate), and H2PO4- (dihydrogen phosphate).
Commonly used chemicals for the nutrients include potassium nitrate, calcium nitrate, potassium phosphate, and magnesium sulfate. Various micronutrients are typically added to hydroponic solutions to supply essential elements; among them are Fe, Mn, Cu, Zn, B, Cl, and Ni. Chelating agents are sometimes used to keep Fe soluble.
The question regarding how to manufacture this nutrients in the Moon is still a question without answer. However, how to save water means to use aeroponics: growing plants in an air/mist environment with no soil and very little water.
Aeroponics is the type of hydrophonics that economizes 98% of the water. It means in essence to spray the roots of the plants with the nutrient solution. NASA has been using this technique in experiments with the space shuttle and International Space Station since 1990.
Aeroponic systems are much better with the oxygenation of the plants roots. Oxygen/air intake is very important to growing healthy plants. Both the mist or fog allows the root systems to grow a lot of fine hair like extensions on the roots because of the small particle sizes of the water droplets. This significantly increases the surface area of the root system, and allows the roots to uptake both the nutrients and oxygen/air more efficiently than they would in a typical hydroponic system. This factor also allows the plants to grow faster than they would in a typical hydroponic system.  Gee whiz, and I thohugt this would be hard to find out.