Both loop diuretics and thiazides can cause hypokalemia by:
Diuretics prevent the reabsorption of Na+-more amount of Na+ reaches the distal poion of the nephron i.e. late DT and collecting ducts. Na+ is exchanged with K+ and H+ Increased distal delivery of Na+ results in more exchange and thus hypokalemia
Inhibiting proximal tubular K+reabsorption
Inhibiting Na+-K+-2Cl-cotranspo in the ascending limb of loop of Henle
Increasing the availability of Na+in the distal tubular fluid to exchange with interstitial K+
Potentiating the action of aldosterone
Kidney