What water temperature should you mix shampoo with?
It's best to dilute shampoo or conditioner using warm water rather than cold, or hot. Warm water mixes in better with most shampoo and conditioner concentrates. Shampoo may not mix with cold water, and very hot water can increase the speed that bacteria grow.
Some conditioner tends to be quite thick, so some can be harder to fully mix in to the water than others, so a combo of warm water plus a stick blender is a handy way to get it properly mixed in if you find that happens.