Two drinking water lakes of Hyderabad - Osman Sagar and Mir Alam, were studied for their chemistry for two years (1977-78). Mir Alam, the older of the two, showed higher silicate content. Dissolved component formed 91-27% of the total silicate content in these lakes. Osman Sagar showed higher percentage of particulate silicate, is to be considered seriously, and would be a threat to the lake in the long run.