The treasurer of the state of Idaho, the city council or city commissioner of every city, the board of trustees of every village, the board of county commissioners of every county, the board of commissioners of every highway district, the board of trustees of every school district, the board of commissioners of every drainage district, the board of directors of every irrigation district, the board of trustees of every library district, and the governing board of every taxing district within the state of Idaho, whenever there is in any sinking fund, now existing or hereafter created by authority of the laws of the state, an amount in excess of the requirements to pay bonds maturing within the current year, shall, so far as practicable, invest the same in time certificates of deposit of public depositories, interest-bearing general obligation bonds, tax anticipation notes or treasury certificates lawfully issued by the United States of America, the state of Idaho, or any city, county, highway district, or school district in the state of Idaho. The state or any city, village, county, highway district, school district, drainage district, irrigation district, library district, or any other taxing district in the state of Idaho may purchase for the sinking fund any bonds originally issued or assumed by it and keep the same alive in the sinking fund and resell the same, or any other investments of the sinking funds, when it may be deemed advisable to make more advantageous investments or to provide means for the redemption of maturing bonds; provided, that if any bonds so purchased are not necessary for the protection of any such sinking fund the governing board shall cause any such bonds together with the interest coupons thereon to be cancelled; provided, that whenever there is in any sinking fund of any irrigation district, now existing or hereafter created by authority of the laws of the state, an amount of funds in excess of the requirements to pay bonds maturing within the current year, such irrigation district may invest such excess moneys in any of the anticipation notes or warrants or other interest-bearing securities of such irrigation district; provided, further that any county hospital board may invest in short term interest-bearing bonds and other evidences of indebtedness of the United States, time certificates of deposit of public depositories or savings accounts insured by the federal deposit insurance corporation, to the extent of such insurance, whenever there are current expense funds in excess of requirements for the current year when it may be deemed advisable to put surplus current funds to work.