Could Pollution indicators such as degree of contamination index (Cd) and potential ecological risk index (PERI) proposed by Hakanson (1980) also considered for water samples to represent surface water quality???
The existence of heavy metals as background levels in sediments differs about what suggested in the background amount in water, so you cannot be used for potential ecological risk index. Assessment of water quality can be done by WQI as mentioned in many textbooks and researches.