(enactment and implementation of Edwards Aquifer Act substantially advanced legitimate governmental interest and did not deprive defendants of all economically viable use of their property, but did unreasonably impede defendant's use of farm as pecan orchard because irrigation permit approved withdrawal of water for irrigation at less than sufficient amount which constituted regulatory taking, and outright denial of second permit on separate tract also constituted regulatory taking; trial court awarded compensation on tract where permit denied (tract 1) in amount of $134,918.40 based on difference in value of dry land farm in county and comparable irrigated farm; compensation for regulatory taking on tract where permit authorized for water withdrawals in insufficient quantity (tract 2) determined to be $597,575 based on market value per acre-foot of water denied; on appeal, court affirmed trial court finding that implementation of Act resulted in regulatory taking, but reversed trial court on computation of compensation owed defendants; appellate court determined that compensation on tract 1 to be computed as difference between value of land as commercial-grade pecan orchard with unlimited access to Edwards Aquifer water immediately before implementation of Act and value of land as commercial-grade pecan orchard without access to Edwards Aquifer water immediately after implementation of Act; compensation for tract 2 to be determined as difference between value of land as commercial-grade pecan orchard with unlimited access to Edwards Aquifer water immediately before implementation of Act and value of land as commercial-grade pecan orchard with access to Edwards Aquifer water limited to 120.2 acre-feet of water immediately after Act implemented).