The problem here is people relying on unsustainable sources of water and then using that water very inefficiently. Relative to farming, cleaning solar panels is a drop in the ocean. In terms of surface area, it doesn't really compare. And of course it doesn't help that people just let the excess water drain away. They pump it up, use it and, then it drains away to rivers and eventually the ocean. Instead, they could be recycling that water and using it for irrigation. But because the water is cheap, nobody cares about it. So it's drained and lost.

In the Netherlands which, depending on how you look at it, is technically mostly a swamp with really awesome drainage and pumps, we have ground water shortages. Reason: farmers like irrigating their land (much of it below sea level) with ground water because it is cheap. But they also like to keep their fields well drained so their plants don't rot in the field. So they are actively draining water from their lands while using ground water to keep them at just the right level of wetness. They use massive amounts of water and the drained water is rich in phosphates and other nutrients which is causing all sorts of issues down stream.

Not sustainable. The climate in the Netherlands while changing is still quite wet. And besides, two of the largest rivers in Europe flow through the country. Mostly we have issues with water levels of those being way too high, not too low. In other words, there's plenty of water. Except in the ground. Getting rid of excess water is actually a major engineering challenge.

Water companies are also tapping into the same unsustainable sources because its cheap and doesn't need a lot of filtering because it's also clean. So there are water shortages and calls for people to use less water, irrigate their lawns and gardens less, and take shorter showers all while we are dealing with getting millions of tonnes of excess water to the North Sea.