For just about any commercial or residential building, the only suitable (IMO) use for graywater would be toilets, and it's not particularly suitable for toilet

For just about any commercial or residential building, the only suitable (IMO) use for graywater would be toilets, and it's not particularly suitable for toilets with a tank, so that rules out just about all residential. The article also uses the term 'purified' which is non-specific. All sorts of things end up in water: soaps, detergents, drain-o, medications, you name it. You can't just distill it, some chemicals are volatile. You can't just filter it, some contaminants will pass through. On a city-wide scale, it only introduces more problems. Having pressurized gray water would require an entire new set of lines, and hopefully the people installing them don't accidentally connect the lines to the wrong distribution (it will happen inevitably). So yes, it's a feel-good story, but it's nonsense. No way to capture the economies of scale, and the water isn't suitable for most uses.