For optimal performance of the 90 cm Bubble Fish Lamp, we highly recommend using distilled water only (or boiled water cooled down). When the lamp is not in use for extended periods of time, please ensure that all water is fully emptied and allow the unit to dry completely. If water is left inside the lamp for extended periods without operation, it may cause damage to the internal circuit board, which can result in the bubble function no longer working. Following these guidelines will help maintain the longevity and proper functioning of the product.