A capital improvement project undertaken by a charter city to extend that city’s water, sewer, or storm drain system or similar system to a disadvantaged community in an unincorporated area shall be considered a public work for the purpose of Section 1720 of the Labor Code, but any subsequent project to construct, expand, reconstruct, install, or repair such systems that have been so extended and that are conducted within that city’s political boundaries shall not be considered a public work for the purpose of Section 1720 of the Labor Code as a result of the extension. For the purpose of this section, “disadvantaged community” means a disadvantaged community as defined in Section 79505.5.