This seems kind of like a bullshit excuse where they just didn't really want to fix the issue. There are a number of waterless cleaning systems that have been available for years, for example [1]. Additionally, why the hell would you throw away the water used for cleaning? Filtering the dust particulate out of the water is pretty straightforward (hell, you can go from muddy to fairly clean water with nothing more than a cotton t-shirt), then you reuse it to clean more panels. 1L/panel with even basic reclamation is ridiculous.