Exemption from taxation for water and electricity by inter state river authorities requires presidential assent for state laws. Exemption from state taxation covers water and electricity managed by authorities for inter state rivers and river valleys, and pre existing State laws shall not impose such taxes except as the President may order. State laws imposing such taxes are effective only after being reserved for and receiving the President's assent, and any delegation to fix rates or incidents requires the President's prior consent to the rules or orders.