a body divided by division baffles into a preset number of intercommunicating chambers, inside of which can be housed various filtration elements so that during a filtration process, water follows a zigzag route;

an infeed point for the water to be purified;

a temperature regulation unit; and

a pump enabling the recirculation of the water;

wherein the body is contained entirely within the tank, wherein the filtration elements are positioned between at least one pump and at least one infeed point to enable entry of the water into the filtration system mainly from below upwards and outfeed of the water from the system from above downwards, and wherein said filtration elements comprise at least a mechanical filtration element and a biological filtration element, each mechanical filtration element being placed upstream of a respective biological filtration element, characterised in that each mechanical filtration element and each biological filtration element is housed inside a distinct chamber and in that an open air space is provided above adjacent mechanical filtration elements and biological filtration elements, whereby the water flowing inside the filtration device in operation contacts air while flowing from a chamber housing a mechanical filtration element to the adjacent chamber housing a biological filtration element.