Natural water is collected, filtered through a 0.45-mu m membrane filter to remove particulate matter, and acidified. Ferric chloride solution and ammonium acetate buffer are added to the water. The pH is adjusted to 3.0 and solid ammonium pyrrolidine dithiocarbamate (APDC) is added to cause coprecipitation. The resulting precipitate is collected on a 25-mm-diameter membrane filter of 3.0-mu m pore size. The filter is placed between layers of the X-ray cell film on a holder for X-ray fluorescence determination of copper, lead, zinc, cobalt, nickel, cadmium, molybdenum, and uranium. Determination of the eight elements in a single water sample in the parts per billion range is well suited for hydrogeochemical prospecting surveys.