The cost of any public work or improvement for the purposes of RCW 35.22.620 and 35.22.640 shall be the aggregate of all amounts to be paid for labor, material, and equipment on one continuous or interrelated project where work is to be performed simultaneously or in close sequence: PROVIDED, That the cost of water services and metering equipment furnished by any first-class city in the course of a water service installation from the utility-owned main to and including the meter box assembly shall not be included as part of the aggregate cost as provided herein. The breaking down of any public work or improvement into units or accomplishing any public work or improvement by phases for the purpose of avoiding the minimum dollar amount prescribed in RCW 35.22.620 is contrary to public policy and is prohibited.