Lamda process and apparatus for purifying water

The invention relates to a process and apparatus that treats waste water, in particular waste water containing surfactants and including grey water, for local reuse. According to the invention, the process comprises a) collecting waste water in a reservoir; b) injecting gas into waste water from the reservoir to form bubbles in the waste water; c) separating the bubbles, and any entrained contaminants, from the waste water; d) drying the separated bubbles and returning any water recovered from the dried bubbles to the waste water undergoing treatment; e) optionally repeating steps b) to d) to achieve the desired purification of the waste water; and f) collecting the purified waste water. The invention provides a robust process and a mechanically simple apparatus that does not require regular replacement of chemicals or filters, yet is capable of treating waste water locally, and in particular grey water for household reuse