Mine also needs cleaning at least weekly because of the five cats. The area where the pump is - like CCL said - tends to accumulate gunk and hair. It always makes that gurgling sound when the water is low. I have noticed lately that I have to add LOTS of water each day - I think partly because they drink so much and partly because of the dry air from the heat. That fountain is also a humidifier for the air

If it seems plugged - it likely needs a good cleaning and a new filter. That filter can clog enough that no water can get through. I am having to change mine about every two months.