The invention relates to an automatic purification water tank, which comprises a first water storage device vertically arranged, a second water storage device vertically arranged, a waste water precipitator and a filter device. The first water storage device is provided with a water inlet used for introducing an outside water source. The waste water precipitator is provided with a drain outlet, and a water inlet end and a water outlet end communicated mutually; the drain outlet is formed between the water inlet end and the water outlet end. The water inlet end is communicated with the first water storage device; the water outlet end is communicated with the second water storage device. The second water storage device is provided with at least one water outlet; the filter device is arranged between the drain outlet and the lowest water outlet. The automatic purification water tank can be used for purifying water and storing the water, and the drain outlet is formed, so that waste water at the filter device can be drained, and the service life of the filter device is prolonged.