You’re still flushing about* the same amount of water out of the pipes though. It just takes longer with a water efficient shower head. And as the parent poster

You’re still flushing about* the same amount of water out of the pipes though. It just takes longer with a water efficient shower head. And as the parent poster points out this is solved by using smaller pipes. * some of the hot water may cool while you wait so there may be a marginal amount of extra wastage at the outset.