If the pH is less than 6.5 or higher than 7.5, you will leach copper or iron (though iron leaching decreases sharply as pH rises) from pipes, and copper, zinc and lead from brass and bronze fittings, and of course, older solder. You can pickle the brass to remove most of the lead and lose copper and zinc on the surface, but over the years (15-20 in drinking water with neutral pH), the next layer of copper and zinc (brass) will also dissolve away exposing new lead. In typical low pH hydroponics solutions, leaching will be much faster than drinking water.While plants need copper and iron, high concentrations will stunt growth of both root and vegetation. Plants are less sensitive to iron than copper and iron leaching generally requires a pH below 5, but it will leach above 5 too and become toxic.
