Methods to quantify lead(II) concentration in water on the ppm/ppb level
Russian interstate standard GOST 18293-72 "Drinking water. Methods for determination of lead, zinc and silver content" (PDF in Russian) suggests to use sulfarsazene (plumbone), which forms orange-yellow complex with lead(II).
Reported method sensitivity (spectrophotometry): $\pu{0.5 μg L-1}.$

A brief review in English [1, p. 315]:


  To determine lead in solid particles of industrial facilities, natural waters, biological objects and salts, sulfarsazene is used (4''-nitrobenzene-1'',4-diazo-amino-1,1-azobenzene-2''-arsono-4-sulfoacids).
  While it is less sensitive than dithizone , it has a number of advantages: it is water-soluble, easy to handle and needs no cyanide as masking agent.
  But, it has insufficient reaction selectivity.
  Manganese, nickel, copper, zinc, mercury, cadmium, iron, zirconium, and other elements interfere with the determination. The methods developed on the basis of sulfarsazene require a preliminary ion separation; for instance, lead is separated by extracting with dithizone solution in carbon tetrachloride …
  
  Study of the reaction of sulfarsazene with lead ions points to simultaneous participation of the lead cation with triazene and arson groups in complex formation.
  Polarographic investigation confirmed the existence of lead bonds with the o-arsonotriazene group of the reagent, and cleared up the azo-group contribution to the formation of the complex which may be due to coordinative bonding with lead atoms.
  The role of the nitrogroup as an electrophilic substituent that improves the mobility of the hydrogen atom of the aminogroup was experimentally confirmed.
  The structure of the resultant compound is as follows:
  
  


GOST 18293-72 also includes polarographic method for lead detection using the dropping mercury electrode.
Reported method sensitivity: $\pu{10 μg L-1}.$

References


Roeva, N. N.; Savvin, S. B. Spectrophotometric Determination of Minute Lead Contents of Natural and Industrial Objects. Reviews in Analytical Chemistry 1986, 8 (4). DOI: 10.1515/REVAC.1986.8.4.313.