▁to ▁put ▁together ▁some ▁legal ▁instructions ▁concerning ▁them . ▁Also ▁it ▁shows ▁that ▁from ▁the ▁nin th ▁to ▁ele vent h ▁centuries ▁the ▁q an ats ▁that ▁were ▁the ▁hub ▁of ▁the ▁agricult ural ▁systems ▁were ▁also ▁of ▁interest ▁to ▁the ▁government . ▁A part ▁from ▁The ▁Book ▁of ▁Alg h ani , ▁which ▁is ▁considered ▁as ▁a ▁law ▁book let ▁foc using ▁on ▁q an at - related ▁r ul ings ▁based ▁on ▁Islam ic ▁principles , ▁there ▁is ▁another ▁book ▁about ▁ground water ▁written ▁by ▁Kar aj i ▁in ▁the ▁year ▁ 1 0 1 0 . ▁This ▁book , ▁entitled ▁" Ext raction ▁of ▁H idden ▁W aters ", ▁exam ines ▁just ▁the ▁technical ▁issues ▁associated ▁with ▁the ▁q an at ▁and ▁tries ▁to ▁answer ▁the ▁common ▁questions ▁such ▁as ▁how ▁to ▁construct ▁and ▁repair ▁a ▁q an at , ▁how ▁to ▁find ▁a ▁ground water ▁supply , ▁how ▁to ▁do ▁level ing , ▁etc .. ▁Some ▁of ▁the ▁innov ations ▁described ▁in ▁this ▁book ▁were ▁introduced ▁for ▁the ▁first ▁time ▁in ▁the ▁history ▁of ▁hydro ge ology , ▁and ▁some ▁of ▁its ▁technical ▁methods ▁are ▁still ▁valid ▁and ▁can ▁be ▁applied ▁in ▁q an at ▁construction . ▁The ▁content ▁of ▁this ▁book ▁implies ▁that ▁its ▁writer ▁( Kar aj i ) ▁did ▁not ▁have ▁any ▁idea ▁that ▁there ▁was ▁another ▁book ▁on ▁q an ats ▁compiled ▁by ▁the ▁cl erg ymen . ▁ ▁There ▁are ▁some ▁records ▁d ating ▁back ▁to ▁that ▁time , ▁sign ifying ▁their ▁concern ▁about