Some companies try to avoid the condenser issues by putting an heat exchanger cooled by water in the refrigerant loop. In Arizona they were sold as "Hot Tap" hot water from cold air. Again water is corrosive and they lost a lot of compressors from leaks in the exchangers. Worked with a guy that used his swimming pool as a pre cooler for his ac's. He was using stainless steel marine exchangers, Still lost a compressor every couple of years due to leaking. Finally disconnected the system.

I installed a heat recovery unit to my ac 2 years ago and it works great. I turn off water heater from may to September. The really hot days the temperature would not go below 85 on those days when the night and day temperature would stay above 90 after heat recovery it would cool to 74 no problem. Increased tonnage effectively and free hot water awesome!

There's another way to cool the condenser on an AC system. If the condenser air were drawn through a swamp cooler, the moisture in the air is still in the gas phase and would not condense onto the condenser coils since they are at an even higher temperature. Plus, using a water softener to treat the makeup water for the swamp cooler would remove much of the mineral content. The same concept could be used for the swimming pool idea. Pump the water through an air handling coil to lower the air temperature entering the AC condenser. These ideas are less effective than direct spray cooling or liquid-to-liquid cooling, but you will avoid the leakage and corrosion issues.

How could anyone not expect damage from city water being constantly sprayed on their condenser. I suspect we've all seen corrosion from yard sprinklers. They used to make "slab" style evap coolers to fit on the side draft condensers in my area. There are still some in place but non functional. Haven't seen any coil damage but I doubt any were in use long enough to cause damage. The thing with swamp coolers, of any type, is they require quite a bit of cleaning and maintenance and these probably weren't maintained at all. Pumps quit, pads fell apart so they were abandoned. With treated water (like water source heat pumps) the concept is good. But I also think there is no cost effective way to regulate everything properly. I did some tests once with spray and watched the amp draw and head pressure drop impressively. But I suspect careful regulation would be essential. Dropping the head pressure too much, say on a milder temp day, could possibly get liquid refrigerant back to the compressor, slugging it. Therefore I think any long term, effective system would have to be pretty sophisticated. What about multi-speed fan motors? Aren't any companies using those? I remember some old systems with two speed motors and temp sensors.

My Dad was a mechanical and nuclear engineer. We lived in Phoenix AZ. In the mid 70's he retro fitted a "swamp cooler" to blow pre cooled air into the AC condenser. He made some tweaks to the swamp cooler because the fan blew faster than the intake fan on the condenser. He made sure it was calibrated fairly evenly. Anyway, the electric bills went down tremendously. Water bills were only slightly higher AND when the home was sold, the AC unit was 32 years old and still going strong! Imagine 32 years in the Arizona desert with 100 or more days above 100 degrees a year and to get 32 years of live out of the AC!

Distilled water is corrosive to many metals. Acid rain caused by high levels of pollution is corrosive. Moist rain, snow and water from municipal systems is not. Water on metal exposed to air does cause oxidation. Recognizing this, all residential AC condensers are made of aluminum alloy, an alloy that naturally and slowly forms a protective water insoluble coating of oxide. The slight amount of minerals that a hard water filter doesn't remove could potentially become an issue if the mist were sprayed directly on the condensing coils. But consider that automotive radiators and ac condensers are made of the same aluminum alloys as house AC condensers, but are more fragile. The spray off concrete roads has a much higher amount of calcium and magnesium salts than most municipal water supplies. Yet most car AC condensers last in excess of 10 years and the most common reason for their failure is not external corrosion but mechanical damage. A far larger threat to the life expectancy of a home AC unit condenser than water damage is not servicing it annually to remove accumulated debris and soil.