The volume of water to be used for fixing the charges for nonresidential establishments shall include any and all water purchased from public or private water companies or both and all water obtained from all other sources as determined by meters installed and maintained by public and/or private companies; by meters installed and maintained by the property owner as may be approved by the city or by estimates or measurements made by the city where metering is deemed impractical. Water used solely for irrigation or such other use which does not enter the sanitary sewer system may be excluded provided such water is separately metered or not metered and the use of such water is completely separated from the sanitary sewer system. (Ord. 166 §10(B), 1970).