(b) The legislature may provide by law for subsidized loans and grants from the proceeds of Texas water development bonds to provide wholesale and retail water and wastewater facilities to economically distressed areas of the state as defined by law, provided, the principal amount of bonds that may be issued for the purposes under this subsection may not exceed $250 million. Separate accounts shall be established in the water development fund for administering the proceeds of bonds issued for purposes under this subsection, and an interest and sinking fund separate from and not subject to the limitations of the interest and sinking fund created for other Texas water development bonds is established in the State Treasury to be used for paying the principal of and interest on bonds for the purposes of this subsection. While any of the bonds authorized for the purposes of this subsection or any of the interest on those bonds is outstanding and unpaid, there is appropriated out of the first money coming into the State Treasury in each fiscal year, not otherwise appropriated by this constitution, an amount that is sufficient to pay the principal of and interest on those bonds issued for the purposes under this subsection that mature or become due during that fiscal year.