Note the following is not cost effective for most people. I did it anyway. We have a swimming pool. Water in a pool in this area evaporates. I've read that a central air system in our area generates between 10 and 15 gallons of condensate a day. Our houses are designed to route that condensate into the sanitary sewer line, usually via a bathroom sink drain. We have central air and also a whole house dehumidifier. I've had the condensate from the larger evaporator coil (we have two but one is not practical to reroute) and from the dehumidifier routed to a rain barrel outside and then via an attached faucet and water hose to the pool. The rain barrel is used to accumulate the condensate during times of high rain and then later empty into the pool.
According to the CDC, A/C condensate is suitable for most non-potable water uses. Some people use that water for gardens and potted plants. Rice University uses that water in its A/C water towers. Of course, putting the water in a swimming pool subjects it to our usual chlorine disinfectant. I've tested our condensate, and it has -0- iron or heavy metals and a pH of 5.5. The slightly acidic water helps (ever so slightly) with bringing rain and tap water down to a recommended pool pH of 7.2-7.8.
So twelve gallons a day doesn't completely replace adding tap water to compensate for evaporation, but it does reduce it a bit. I figure based on our highest Katy water tier pricing, it will save maybe $20 a year. It cost me $100 to the A/C tech plus the rain barrel to reroute the condensate. If done as part of new construction, it could really cost almost nothing. It does save 300 gallons of treated Katy water a month. If there were, say, 300 pools in Katy, that could save 90,000 gallons a month or a million gallons a year. It's not saving the earth, but it's a little something. A good cover could reduce evaporation, but the shape of our pool makes that impractical.