Section 18(1)(iii) in The Bengal Agricultural And Sanitary Improvement Act, 1920
(iii)apportion the share of such cost recoverable from the landlords or tenants, or both, or different classes thereof, according to such rates as may be determined in the prescribed manner, having regard, so far as practicable, to the degree of benefit derived, or estimated to be derived by the different areas and classes affected by the scheme.