(e) A landlord may not charge the tenant of a dwelling unit separately for water usage measured by a submeter, nor allow such tenant to be so charged, unless the submeter measures only water that is supplied for the exclusive use of the particular dwelling unit and only to an area within the exclusive possession and control of the tenant of such dwelling unit and does not measure any water usage for any portion of the common areas or by any other party or dwelling unit; provided further, that a landlord shall not charge such tenant for water supplied through a submeter to the dwelling unit prior to the landlord installing fully functional water conservation devices for all faucets, showerheads and water closets in the dwelling unit; and provided further, that the landlord shall ensure that such water conservation devices are installed and functioning properly at the commencement of each subsequent tenancy in such dwelling unit.