It seems like such a huge amount of water and would require so much energy to get it that high, plus there’s the waste to deal with
Toilet waste (black) water pipes are quite underused for their diameter so it’s enough to just feed dozens of bathrooms’ worth into a reasonable diameter you can still get at a hardware store. Sure, some will have trouble flushing if they all do that at the same time but not too serious.
As for drinking water, some high-rises feature tanks as part of their oscillation damping system anyway, and municipal water towers don’t need to be placed much higher than customers to get decent pressure. I think it’s not the amount but pressure of water at the ground floor that causes engineering challenges. The pumps and tank at the top help, though.
