Many products that are found in a typical household may be acidic or basic.  The pH value indicates the strength of the acid or base.  The pH scale ranges from 0 to 14 with 0 being the most acidic and 14 being the most basic.  Warnings on certain products may be due to the fact that the product is a relatively strong acid or base.  Strong acids and bases completely ionize when brought into contact with water, providing numerous acid ions or base ions to the solution.  Many of the products we pour down the sink, that then end up in the ground water, are strong acids or bases.  For a substance to be neutral, it must have a pH of exactly 7.  Although pure water (pure $$\ce{H2O}$$) is neutral, some sources of water may have a pH other than 7.  In fact, some brands of bottled water have an acid level that would categorize the water as “acid rain”.