Hydroponic or soil? pH is much more important to a chemical hydroponic garden than an organic soil one. In any event, your tap water is slightly basic (over 7), and your plants like it slightly acidic (6.2-6.5 ish). To make your tap water more acidic, add an acid (lemon juice, vinegar, or any of several acids), or a "pH Down" product, which is a refined acid of some sort.