The only reason to thin any paint is to get the viscosity down so that spray gun can work properly and to a lessor extent influence how the film forms on the object being painted.
Water based acrylic latex paints may need thinning or flowability additives for spraying only.
In spraying, as the droplet passes through the air, some of the added water is evaporated. Adding excess water for other reasons affects the ability for a good film to form on the object. If you are not spraying, do not thin paint unless manufacturer’s directions specify to do so for brush or roller based application.
Organic solvent based coatings may need drying accelerators or other additives, but that does not seem to be the question.
Bottom line, if spraying, try without thinning first. If a different orifice diameter in the gun does not help, then thinning no higher than the manufacturer’s guidance may be used.