Catalyzes the irreversible hydrolysis of pyrophosphate (PPi) to phosphate. diphosphate + H2O = H(+) + 2 phosphate Strongly inhibited by Ca(2+). At least 2 separate genes code for soluble pyrophosphatases in potato. This protein is probably encoded by the Ppa1(a) locus located on chromosome 12. Belongs to the PPase family.