Air conditioning and some heating systems generate huge amounts of recoverable condensate.
I would propose a building or facility condensate recovery and treatment system for primary drinking water (the most valuable use of water) with excess going to irrigation of green systems.
I have no doubt that it will be a combination of systems which will make the ideal plan for saving water. The real feat will be to formalize an engineered matrix of solid technologies which will work together for a facility in a unique environment. Two identical buildings, one in Phoenix, one in Minneapolis, would use completely different water saving technologies because of environment and seasonal variations.
My proposal would happily support other technologies like, green walls, roof top gardens, landscape irrigation, but most importantly, drinking water.
Drinking water requirements are the highest value added use of reclaimed water. Drinking water must be clean, filtered, and treated for delivery through a facility. Air conditioning condensate represents a huge amount of water, is realtively clean and would require minimal filtration and treatment to be used for drinking water within the facility that generates the condensate. Many cities have central heating systems call District Steam heating, often the condensate is not reclaimed even though it is as pure as distilled water. This water could be added directly to the dirinking water supply.
If a facility produces more fresh water through recovery and treatment than is consumed, it could pump to the water main and receive a credit.