Water quality parameters comparison

Hi All

The WHO defines, "Petroleum products" as Petroleum products are used in large quantities, primarily as fuels. They are complex mixtures of chemicals derived from crude oil by distillation and fractionation. They consist primarily of a wide range of aliphatic and aromatic hydrocarbons, many of which are of extremely low solubility in water. Petroleum products are widely stored and handled and are often spilt. The primary concern for drinking-water is the potential for spills into source water, penetration of distribution systems and contamination of drinking-water treatment works.

I am confused with a similar term, "Dissolved Hydrocarbons" which I came across a water project recently.  The potable water quality of the project in question described "Dissolved Hydrocarbons" with a guaranteed level of < 0.01 mg/L, with a rider that, " The taste and smell threshold value varies widely according to product and it is 0.0005 ppm (mg/L) for hydrocarbons and distillate "

My questions to all are as follows:-