Before imagining how green your garden will be with graywater irrigation, it is vitally important to determine how much graywater your household generates each month.
As a guide, each person generates 25 gallons of graywater per day from shower / bath and laundry. This adds up to 750 gallons per month.
Garden generally require between 1 gallon (clay soil) and 4.5 gallons (sandy soil / gravel) per square foot per month. We will assume 2 gallons per square foot per month (loam) for our examples.
Therefore for one person, we can irrigate 750 (gallons per month) / 3 (gallons per sq ft per month) = 375 square feet of garden beds, without additional top up.
Using the same figures as above, a family of 4 could irrigate 1,500 square feet of garden beds.
Clearly using all of the graywater generated by 4 people living on a small block will result in over watering. Conversely, attempting to irrigate 2,000 square feet with graywater generated by 2 people alone will result in under watering.
The following case studies show different techniques used to cope with site specific issues.