Pyrophosphatase that catalyzes the hydrolysis of nucleoside triphosphates to their monophosphate derivatives, with a high preference for the non-canonical purine nucleotides XTP (xanthosine triphosphate), dITP (deoxyinosine triphosphate) and ITP. Seems to function as a house-cleaning enzyme that removes non-canonical purine nucleotides from the nucleotide pool, thus preventing their incorporation into DNA/RNA and avoiding chromosomal lesions. H2O + XTP = diphosphate + H(+) + XMP dITP + H2O = dIMP + diphosphate + H(+) H2O + ITP = diphosphate + H(+) + IMP Binds 1 Mg(2+) ion per subunit. Homodimer. Belongs to the HAM1 NTPase family.