How much water is wasted when waiting for the hot water faucet to come out with hot water?

                         In most residential households, typically there are hot and cold water faucets, in showers, bathroom and kitchen sinks. But it takes time and lots of water wasted while waiting for hot water to come out. It takes at least half-gallon and more in showers before hot water come out. Multiplying this by millions of household hot water fixtures, it could fill a small lake. Why not install tempered water fixtures instead in bathrooms. I installed a miniature hot water recirculating pump so I get hot water soon as turn the faucet on.