The pH of the water will increase if MgOH (presumably you mean Mg(OH)₂ - Magnesium hydroxide) is dissolved in it. Here's why:

* Magnesium hydroxide (Mg(OH)₂) is a base. It dissociates in water to form magnesium ions (Mg²⁺) and hydroxide ions (OH⁻).

* Hydroxide ions (OH⁻) are responsible for the alkalinity of a solution. The higher the concentration of OH⁻, the higher the pH.

* Therefore, dissolving Mg(OH)₂ in water will increase the concentration of OH⁻ ions, leading to a higher pH (more alkaline solution).

In summary:

* Mg(OH)₂ is a base.

* Bases increase the pH of a solution.

* Dissolving Mg(OH)₂ in water will increase the pH.