Did they say it was efficient? The "closed loop" is only one part of the system that cycles water between the heat exchanger and the building/servers.

The second part of the system is an open loop that uses water to cool the closed loop at the heat exchanger.

The Dalles data centers use a large fraction of the water supply of The Dalles because the data centers are extremely large and the town of The Dalles is of negligible size. It is also true that the paper mill of Valliant, Oklahoma uses 50 million gallons of water per day and that the town of Valliant, Oklahoma, population 819, uses less than 1% of that amount, so the paper mill can be said to be using > 99% of the local water supply but this is also a meaningless comparison.

So we'll move the datacenters from the tiny town to just outside of a giant city which will probably move that percentage down to only a few percent if even that. Problem solved!

You're looking at the wrong metrics to compare here if we're trying to just gauge how efficient a datacenter is or is not. This metric could be useful if the datacenters are attached to the municipal water system and thus begin to be a massive load compared to what was originally planned/built, but in terms of understanding the total water use compared to other industrial users its kind of a meaningless statistic.