It completely depends on what's in your local tap water. Generally Phosphate is added to protect you plumbing so PO4 will be very high. In some locations Copper is added to the reservoir to kill off excess algae. Copper is a Major concern with reef aquariums. It is toxic to nearly every salt water animal at levels barely above Natural salt water levels.
Silicates, Nitrate, Chlorine, zinc & ammonia are other concerns.