Gray water is not as clean as rainwater, or even as clean as stormwater. We can expect a steady flow of suspended and dissolved organic material, plus the byproducts of the cleaning chemicals. However, the water is safe for many uses.  The simplest is turf irrigation. Most plumbing codes do not require treatment of gray water, when used for irrigation, provided that the water is used within 48 hours. This can be accomplished automatically, using an irrigation controller. While this does provide irrigation water, it is not the most efficient use of the available water. We must irrigate whether the lawn needs it or not, in order to meet the requirements of the plumbing code (and not allow the water to go septic and stink. Nobody wants a smelly lawn).