(a) Any revenues of the district derived from any source remaining at the end of each fiscal year after payment of all expenses of maintaining and operating the facilities of the district, providing for the renewal or replacement thereof, the acquisition or construction of improvements and betterments to the facilities and the purchase of equipment and furnishing therefor, shall be considered as surplus.
(b) Any revenues of the district may be used by the district for the payment of any expenses incurred in determining the feasibility of a facility or facilities and developing plans therefor, including engineering, architectural, legal, and administrative costs and incidental fees.