(a) Except as provided by this section, a contract for the purchase or construction of materials, machinery, or other things used to constitute the district's works, improvements, facilities, plants, equipment, or appliances must be advertised, let, and awarded as provided by Section 49.273, Water Code.(b) If the district determines, after a contract has been awarded, that additional work is needed or that the character or type of the work or facilities should be changed, the board may authorize change orders to the contract on terms the board approves, provided the change does not increase the total cost of the contract by more than 25 percent.(c) The district must seek informal competitive bids or proposals from at least three bidders if:(1) the estimated amount of a proposed construction contract is more than $5,000 but less than $25,000; or(2) the duration of a proposed construction contract is more than two years.(d) A contract must be written and awarded to the lowest and best bidder. Added by Acts 2009, 81st Leg., R.S., Ch. 1139 (H.B. 2619), Sec. 1.04, eff. April 1, 2011.