We recommend counter-top water filtration systems to renters and people on the budget. They are generally cheaper than under-counter or whole house systems and you can only install them on one tap. You will find two different type of counter-top filters:
Gravity Fed water filters. These typically sit on your kitchen or any other bench in the house and not connected to any water source. You have to manually re-fill them. They are very mobile and you can use them wherever you want them.
Pressurized Water filters. They are the ones connected to your kitchen tap and supply clean water on demand just like wen you open your tap. It is works with a water divergent that send the water through the water filter instead of free flowing from your tap.