Cal. Pub. Res. Code § 5594

All contracts for furnishing supplies, materials, labor, or other valuable consideration furnished the district, for maintenance projects involving contractor services to preserve, maintain, or repair any existing building, structure, or improvement, or for constructing any new building, structure, or improvement, when the expenditures will exceed the applicable amount specified in Section 5549, shall be let to the lowest responsible bidder, after notice inviting bids, published in a newspaper in the district at least one week before the time of receiving bids. The board of directors may reject all bids and readvertise, or by a five-sevenths vote may elect to purchase the materials or supplies in the open market, or to construct the building, structure, or improvement by force account.