 fresh water make-up system is needed. Keep in mind that a major contributor to grey water is the laundry, and that its use is periodic. If you do laundry once per week, you will need a grey water reservoir large enough to accumulate water suffi- cient to carry you over until the next week. More frequent laundry uses will reduce the size of reservoir needed. For large families, fresh make-up water should be available. For those designs which require filtration, the sand filters described in this book are certainly appropriate. In addition to those filters, a number of simpler designs have been proposed for grey ONSITE WASTEWATER DISPOSAL Table 7.4 Water Volumes Associated with Grey Water Systems Water Use Range Bath/shower (gpcd) Laundry (gpcd) Dishwashing (gpcd) Total Grey Water Produced (gpcd) Toilet (gpcd) Net Grey Water Produced (gpcd) Grey Water Reservoir Required (gal/person) assuming one laundry day per week for up to 3 persons. For 4 or more persons, more frequent laundry days are recommended, and a fresh water make-up system may be required. NOTE: gpcd = gallons per person per day. Source: University of Wisconsin data. water filtration. These are adequate for a few tens of gallons per day of grey water. Figure 7.13 shows a few of these designs using 55- gallon drums. Swimming pool filters offer a further possibility. High-rate filters can produce 15 to 20 gal per min of filtered water until the sand clogs up. Cleaning requires provision of clean water for backwashing. Cartridge filters accept from 0.5 to 1 gal per min, and filter elements which can be removed and cleaned. Swimming pool filters operate at around 15 lb per sq in. of water pressure. A functional arrangement is to install a dosing chamber following the grey water tank SO that the dosing pump can push the grey water through the filter and through the distribution system (Figure 7.14). The swimming pool industry can be called upon for disinfection, as well, although there are disinfection units made for domestic sewage disinfection. The disinf