I've also pondered - how do we "waste" water? "Waste" seems to insinuate that the water is no longer water, but that's not really true. If you use water in your home, it is treated and returns to a creek, river, ocean, etc. Still water. If you wash your car or water your lawn, it evaporates as part of the Earth's natural cycle and eventually falls again as rain somewhere else. Still water. The only true "waste" that I could think of involves the use of water in production processes where it changes state, i.e. where it is an ingredient in a chemical reaction that produces a solid product.

In my mind we do a lot of things to move water, which can definitely be harmful on a local and regional scale. But it is still water. Am I wrong here?

From a practical perspective, I think there is a clear difference between seawater or contaminated water that is not usable for most human purposes, and clean freshwater that is usable. Converting the latter into the former without getting much value out of it is "waste" in a practical sense.

Analogy - if you blow $10K on nothing, the money hasn't changed state, but it has left your pocket and you probably call that "waste".

Using heat exchangers to boil sea water is one heck of a challenge. The salts tend to lay down and foul the exchangers in no time flat. That causes hot spots, corrosion, and loss of heat transfer.
The trick is to control the heat and pressure so the water flashes to steam at exactly the right moment and place so you can seperate the salts and dispose of them, but it's much harder than it sounds.

Standard rule of thumb is anything higher than a 250 F delta P requires purified water, 150 to 249 can use chemically treated treated (clean) water.

Some nuke plants use sea water as a coolant, but it's a three stage process from core to condensor.

The core heats pure water to turn it to steam.
That water flows through a heat exchanger where it transfers heat to purified water on the other side of the exchanger and turns it into steam but has no physical contact to prevent contamination.

That steam flows through the turbines where it gives up it's heat, and finally exits the low stage turbines into a condensor.
At that time it is technically still steam but it's around 140 degrees F because its under about 28 inches of mercury worth of vacuum created by the condensor.
Sea water flows through the other side of the condendor where it only has to reduce the temperature about 60 degrees and never goes through a phase change.
it still requires a great deal of backflusing, travelling screens, and other maintenance to keep that condensor relatively clean.

No, not exactly. The concept is called "return flows"

But we don't always use the appropriate level of purification or cleanliness for the task at hand.

Death Valley was a lake 10,000 years ago when it rained a lot more in the west. Geologically, that was yesterday.