(a) The cost of construction properly includible in the water plant accounts shall include, when applicable and when actually incurred, the cost of contract work, labor, materials and supplies, transportation, engineering and supervision, law expenditures, compensation and other insurance and injuries and damages applicable to construction, taxes and interest during construction, permits and privileges, use of construction facilities, cost of keeping construction records, and other analogous elements applicable to the construction and acquisition of water plant. The costs includible in the principal items are:

1. (1) Contract work includes amounts paid for work performed under contract by other companies, firms, or individuals, costs incident to the award of such contracts, and the inspection of such work. The cost of work performed by the utility on projects when part of the work is performed by the utility itself and part is performed by others under contract shall be included as labor, materials, transportation, general administration, engineering services, etc.
2. (2) Labor includes the pay and expenses of employees of the utility engaged on construction work, and also workmen's compensation insurance, payroll taxes and similar items of expense.
3. (3) Materials and supplies includes the purchase price at the point of free delivery plus customs duties, excise taxes, the cost of inspection, loading and transportation, the related stores expenses and the cost of fabricated materials from the utility's shop. In determining the cost of materials and supplies used for construction, proper credit shall be made for unused materials and supplies, for materials recovered from temporary structures used in performing the work involved, and for discounts allowed and realized in the purchase of materials and supplies.
4. (4) Transportation includes the cost of transporting employees, materials and supplies, tools, purchased equipment, and other work equipment (when not under own power) to and from points of construction. It includes amounts paid to others as well as the cost of operating the utility's own transportation equipment.
5. (5) Engineering and supervision includes the portion of the pay and expenses of general officers, engineers, surveyors, draftsmen, inspectors, superintendents and their assistants applicable to construction work and the amounts paid to other companies, firms or individuals engaged by the utility to plan, design, prepare estimates, supervise, inspect, or give general advice and assistance in connection with construction work.
6. (6) Law expenditures includes the general law expenditures incurred in connection with construction and the court and legal costs directly related thereto.
7. (7) Interest during construction includes the net cost of borrowed funds used for construction purposes and a reasonable rate upon the utility's own funds when so used. Interest during construction shall be charged to the individual job upon which the funds are expended and shall be credited to account 1536, Interest Charged to Construction—Credit. The period for which interest may be capitalized shall be limited to the period of construction. No interest shall be included in these accounts upon expenditures for construction projects which have been abandoned.
8. (8) Taxes during construction includes taxes on physical property (including land) during the period of construction and other taxes properly includible in construction costs before the facilities become available for service.