The first part of your shower is always cold and this cold water is being lost down the drain. Save this water with a redwater diverter.
Most households do not have a hot water system / geyser located close to each tap which means it takes time for the hot water to travel through the pipes and arrive hot at the tap.
While you are not using the hot water tap, the water in the pipes cools down so the next time you run the hot water tap, this cool water needs to be pushed through the pipes and is washed down the drain, before the hot water arrives.
This cool water can be saved by installing a Redwater Diverter.
This saved water can be diverted to either a rainwater tank, a header tank in the roof to flush the toilets, a garden, to top up the pool.