Well, Randy and Boomer were always specific and urgent in warning never to add water to acid. If you do a simple search "how to dilute muriatic acid" you will see the same, including from manufacturers, warning of a "potentially violent explosive reaction." I do not know what the data referred to may be, and presumably the warning extends from the diluting process of pure hydrochloric acid (muriatic that is sold is a diluted form).
Me, I will follow the universal instructions!