Answer:
As we all know, HCl is highly reactive acid therefore it is not recommended to dilute it by simply adding water to it. By adding water to HCl, exothermic reaction will takes place and it may cause damage to the experimenter.
In order to dilute HCl, pour HCl in water as water is good absorber of heat and will absorb heat from the exothermic reaction thereby acting safely towards the experimenter.