A great solution to this waste is a hot water recirculation pump. The hot water recirculation pump takes water from your hot water line and pumps it back into the cold line until a desired temperature is reached, then the pump shuts off and when you open your faucet hot water comes out instantly. Installing such a pump can save as much as 17000 gallons of water per year. Here is a diagram.
Depending on the water heater system you have (Tank vs. Tankless) there are 2 different types of pumps available (tankless system requires at least 1 gallon/minute water flow to trigger the heater).
I also recommend you get a pump that has a built in thermostat, so that it shuts off automatically when the hot water is ready to dispense. This will reduce the load on your water heater and not increase your gas/electrical bill too much. It will take as much gas or electricity as needed to heat ~20 gallons of water from ambient temperature of the pipes to 120 F for each time the pump runs. Insulation would definitely help, but it won't keep the temp for long. The pump itself uses 60 Watts of power when it runs (verified with Kill-A-Watt).
The pumps with a thermostat also come with a timer and you can specify the time period in which the pump should operate, the time you need hot water the most (mornings and when you come back from work/school).
The first thing you need to do before installing the system is to pick the location of where the pump is going to be installed at. These are things to consider for the location:
- has an electrical outlet
- is used the most in the house
- is furthest away from the water heater (either check your plumbing plans or time each faucet for how long it takes for the hot water to appear, this you need to do on different days for each faucet)
In my house all three of these happen to be my kitchen sink.
The actual installation is fairly simple. Turn off the water, connect the faucet hoses to the outflow connections on the pump and install new hoses from the water line to the inflow connections on the pump. Plug it in and you are all set. Turn on the water (both hot and cold) at the faucet to let the air out of the system.
I wanted to further reduce the load on my tankless water heater and plugged in the pump into a wifi (WeMo Switch) enabled power outlet, so that I can control when the pump runs from my phone, and to turn off the system when nobody is home and we forgot to turn it off.