There are many reasons including medical, environmental and behavioral, for inappropriate urination.

Medical Reasons

Cats that are experiencing inflammation in their urinary tract — either from an infection, urinary stone or sterile cystitis — can experience strong urges to urinate. Inflammation may cause the cat to urinate whenever the urge strikes. Kidney disease and diabetes can cause cats to drink and urinate excessively.

Litter Box Aversion

If the litter box is not cleaned regularly, the cat may not want to use it, and will seek out a more preferable place to eliminate. Preferred locations are usually soft, horizontal surfaces. In multiple cat households, one cat may guard a litter box and keep the other cats from using it. 

Additionally, if the litter box is placed in a loud or frightening area (like near a furnace) the cat may avoid using it. Defecating outside the box is good sign of littler box aversion. It is suggested to have one litter box per cat, plus an additional box. Also having a litter box per floor can be helpful, especially for older cats with arthritis who may have trouble going up and down the stairs. 

Most cats prefer a litter that closely relates to sand and is unscented.  

Spraying

Urine marking behavior is usually on a vertical surface; the cat will lift its tail, and quiver when marking. Most cats that spray are unneutered males or unspayed females. However, neutered and spayed cats will mark when they perceive a threat such as a new cat in the house, or if they are frustrated with a new diet or inadequate playtime.  

Take Action

Prompt intervention is the key to preventing inappropriate urination from becoming a habit. The first step is to identify the culprit if in a multiple cat household. Secondly, make sure that the litterbox is a clean, comfortable and safe area for elimination. Consider spaying or neutering intact cats if they are spraying. It is also important to rule out any medical causes for inappropriate urination.