Commonly used cardiac drugs. They get rid of water and used in oedema (reduces excess water) and hypertension (reduces fluid and thus pressure in circulation).
Furosemide acts on a Na-K symporter (kicks out K+, reabsorbs Na+). Thus hypokalaemia is a side-effect
Bendroflumethiazide prevents Na+ reabsorption. Thus hyponatraemia is a side-effect. And they can gain calcium, causing hypercalcaemia.
Spironolactone. Seems to be pretty awesome. Gains K+ so hyperkalaemia is a potential side-effect. Works by inhibiting aldosterone.