Protozoa live in seas, rivers, lakes, ponds, decaying matters and soil. Water is a requirement for their habitat and they can exist in diverse regions where this is present.
Protozoa that live in salt water do not require vacuoles, which are structures in the cytoplasm that function in intracellular secretion. The salt concentration inside the cell is similar to the concentration in the sea water and there is no need to contract and empty fluids. Protozoa that do possess these structures and live in less salty conditions empty water through a pore in the membrane and excess fluid enters the cell.