Displaces two of the three amino groups from melamine, producing ammeline and ammelide as sequential products (PubMed:11274097). Can also catalyze deamination of other s-triazines such as CAAT (2-chloro-4,6-diamino-s-triazine) and aminoatrazine (PubMed:11274097, PubMed:12200330). Has no activity with ammelide, atrazine, halo-triazine substrates or with pyrimidines (PubMed:11274097). H2O + melamine = ammeline + NH4(+) ammeline + H(+) + H2O = ammelide + NH4(+) Binds 1 Fe(2+) ion per subunit. Melamine catalysis is highly inhibited in the presence of aminoatrazine. TriA and atrazine chlorohydrolase (AtzA) from Pseudomonas sp. strain ADP are 98% identical but catalyze distinct biochemical reactions. Enzymes differ by only 9 amino acids. These 9 amino acid differences between TriA and AtzA represent a short evolutionary pathway connecting enzymes catalyzing physiologically relevant deamination and dehalogenation reactions, respectively (PubMed:11274097). Potential evolutionary trajectories between AtzA and TriA have been constructed, and catalytic activities of the intermediates along those trajectories have been characterized (PubMed:22768133). Belongs to the metallo-dependent hydrolases superfamily. ATZ/TRZ family.