Upon complying with this chapter, the district may defray the expense of any or all of the improvements by special assessments, including the construction of all or part of an irrigation water supply works or any improvement, extension, or replacement of such works, including the construction and erection of wells, intakes, pumping stations, settling basins, filtration plants, standpipes, water towers, canals, ditches, aqueducts, reservoirs, water mains, and outlets, and all other appurtenances, contrivances, and structures used or useful for a central supply works. In planning an improvement project, the board may include in the plans any and all items of work and materials, which in its judgment are necessary or reasonably incidental to the completion of an improvement project of that type.