Realistically, you should be rotating between both cold and hot water. When cold water touches the surface of your body, your hypothalamus thinks your body internally is cold and therefore takes all measures to increase your body temperature i.e. make hairs on skin surface stand, pump blood faster, goosebumps, decreases sweating to absorb maximum heat from the surroundings.
Doing this continually is not a good idea as though your cold on the inside, your core body temperature increases, not exponentially but its not okay for your body temp to continually increase as this could slow down your metabolic rate as enzymes denature, reducing the amount of nutrients you get due to minor reduction in cellular activity. It could also provide an environment enabling bacteria and viruses to ideally survive and replicate at their optimum temperature. Which is usually why people tend to get sick.
Having showers in hot water is not the best idea either as this will result your body to think your hot, and increases sweat production, flattens hair on skin surface, increases urine production, etc. Which is also a negative impact, as your body temperature lowers, enzyme activity is slower and many
become inactive therefore simple processes such as digestion may not occur to their full potential i.e. not all of your food will be digested giving restricted growth and repair. Also reduced enzyme activity in terms of secreting hormones and phagocytes or lymphocytes functioning properly. Hence why again you get sick.
This is why I prefer rotating between the two. Start at cold and when your body becomes more aware of the changes gradual increase to hot until again the heat is recognised, decrease the temp and vice versa,