Naomi would probably be wary of that! She's avoiding attention and since her job involves a lot of documentation of who's using/doing what when or so says my Google research, using her off time to test tap water without any prior reason to suspect it seems kind of suspicious at a time when the police are looking out for the reincarnates. If someone commissions the lab or if rumors start up that the water's being polluted, though, that's a safer opportunity to start testing.