In my village the water is filtered and chlorinated but completely undrinkable because of residual e-Coli and Clostridium bacteria. Even though everyone here again filters the water at their houses (1 or 5 micron cartridge filters) and then irradiates with UV, it still fails safety tests.
As well as the tests you mention, you also have to sample and incubate on a culture medium for at least 48 hours to allow bacterial colonies to grow and be counted. Dissolved metals are also a problem here and the main cause of failure to be sterilized by UV. High iron levels (here >1800ug/L) causes a shielding effect that stops UV penetrating the entire flow through the equipment and some un-irradiated or partially irradiated bacteria manages to creep through and then grow again.
Brian.