Using non-food grade NaOH for pH control
Iron hydroxide is insoluble, so it will precipitate out. If there are other metals that aren't  alkali metals or alkaline earth metals heavier than calcium, they will also precipitate out. Most of these reactions will release some heat, but if the concentration of the metal ions is low, that shouldn't matter too much.

If you plan to drink the water, using non-food grade $\ce{NaOH}$ might cause a problem, because you won't know what else is in there.

If you add more details, we can probably tell if there are any other things to be concerned about.