evidence: As many as 93,537 "bio-digesters"--as the toilets are called--have been installed in mainline express and mail trains by the Indian Railways. These are small-scale sewage-treatment systems beneath the toilet seat: Bacteria in a compost chamber digest human excreta, leaving behind water and methane. Only the water, disinfected later, is let out on the tracks. [...] During the last three years of the second UPA government (2011-14), 9,350 bio-toilets were fitted in trains but the figure rose by 539%, to 59,735, in the first three years of the NDA government (2014-17). [...] ________________________Railways ministry: "It is not correct to say that bio-toilets in coaches are ineffective or ill-maintained. The waste water discharged from the bio-toilets is tested periodically for specific parameters in order to ensure that the discharged water meets the required norms.