Diuretics cause loss of:

Complications of high ceiling and thiazide type diuretic therapy - Hypokalaemia  This is the most significant problem. It is rare at low doses used for hypertension, but may be of grave consequence, when brisk diuresis is induced or on prolonged therapy, especially if dietary K+ intake is low.  Degree of hypokalaemia appears to be related to the duration of action of the diuretic; longer acting drugs cause more K+  loss.  Hypokalemia is less common with standard doses of high ceiling diuretics than with thiazides, possibly because of shorter duration of action of the former, which permits intermittent operation of compensatory repletion mechanisms. Hypokalaemia can be prevented and treated  by:  (a)  High dietary K+ intake  or  (b) Supplements of KCl  (24- 72 mEq/day) or (c)  Concurrent use of K+ sparing diuretics. Reference: Essentials of Medical Pharmacology Eighth Edition KD  TRIPATHI  page no 631