One other thing to add. Water coolers are mechanically more complicated and less reliable because of it.
Depends on your point of view. The 305 V8 in my 1987 Caballero is vastly more mechanically complicated and yet 33 years later, it's still running just fine.
If you don' t have a performance gain and a specific need for the performance gain water is in my opinion overrated.
Overrated is probably not the right word. Liquid cooling in any form is extremely misunderstood. If it's applied correctly, it's somewhat superior to aircooling. Aircooling is just much easier to get acceptable results.
Just like fans fail so do pumps.
Most fans have an MTBF (Mean Time Before Failure) of about 50,000 hours. Pumps are usually 50,000-100,000 hours. You have to move upto Noctua to get a 150,000 hr fan.
They are not silent and when they fail thermals go to bios shutdown levels.
My nzxt x61 was dead silent, literally needed to stick my head into the pc to hear the hum. Almost all pumps are similar since they are mostly vatients of asetek or coolit designs, and most often totally inaudible over the noise of rad/case fans unless specifically looking to hear it or using uber silent fans on low rpm.
I retired that nzxt when both the fans failed after 6 years 24/7 usage, the pump still going strong. Since most ppl revamp/replace their system in 4-5 years, including a new cpu cooler, longetivity is overrated. Pump failures at that time are often just the excuse ppl use to finally upgrade, which they had planned to do anyway, just never got around to it.
If the fan/s on an aircooler fail, the cpu will also go to thermal shutdown levels, often in less time. Only a fully functional cooler prevents that from happening, doesn't matter if it's liquid or air. On the other side of the coin, if the fans on an aio fail, you'll have plenty of time to shutdown as the rad itself will still be functional as a passive heat exchanger.
AIOs are very popular but I look at them kind of like I look at liquid nitrogen. If you aren't going to aggressively overclock the increased heat exchange characteristics do very little good in normal use scenarios.
Eh, disagree with that I do. Except about the popularity. The function of any liquid cooling is the same as any air cooling, it just does it in a different way. Liquid and air both have drawbacks and bonuses. A major drawback of air is its limited capacity, even mainstream cpus can tax the largest/best aircoolers, with very little OC. Like a i9 9900k/s vs NH-D15 at 5.0Ghz locked core. I can get 5.0GHz on my i7-3770K and not see past 72°C, it's the 9900k/s core count that makes such a massive difference.
And you will not get anything larger than a Noctua NH-U9s in my current case, yet I can stick a 2x240mm rad full custom loop cpu/gpu in it. (nCase M1 v6, mITX uSFF, think shoebox and you'll be close)
Liquid is just as useful and able as air, the biggest real difference is in preference, not ability.