Tex. Water Code § 55.500

In districts organized under Article III, Section 52, of the Texas Constitution, the amount of bonds or the amount of the contract indebtedness with the United States may not be more than one-fourth of the actual assessed value of the real property in the district as shown by an assessment made for this purpose or by the last annual assessment made under this chapter. This limitation does not apply to districts operating under the authority of Article XVI, Section 59, of the Texas Constitution.