It takes about 30 to 45 seconds for my shower to heat up. A lot of perfectly good water goes down the drain while I wait for the water to get up to temperature. Rather than letting this water go to waste, I would like to save this water (for use in watering a garden, if it matters). Of course, I could hold up a bucket to the shower head while it heats up, but I would like a solution that is a bit more automated so that when I turn on the shower the water is automatically stored (for gardening) without any extra effort.
Is there any way to easily achieve this without keeping a bucket in the shower?