direct connection between grey water and food items. Don't grow root crops with grey water without first disinfecting it. Don't surface irrigate where children and other critters have easy access unless the grey water is disinfected. And don't spray-irrigate with grey water even if it is disinfected. The chance of spreading disease is just too great. On the other hand, it may not be necessary to disinfect water meant to irrigate corn or poplar trees. ONSITE WASTEWATER DISPOSAL Grey Water System Valve Black Water System Figure 7.12 Separate grey water tank. Design As mentioned earlier, all of the disposal methods used for com- bined wastewater are available to dispose of grey water. But if the idea is to reuse the water, choose a method designed specifically for that purpose. Review the methods described in the section on Land Application in Chapter 6. A practical means of circumventing a whole category of grey water system problems is to install a septic tank and drain field designed to handle the total wastewater flow. Install a separate grey water tank and connect a two-way valve to the outlet. One outlet pipe then connects to the full-size septic tank drain field and the other connects to the grey water distribution system (Figure 7.12). This design allows loading and resting of the soil at a reduced fre- quency. It also provides control of the times and volumes of water an irrigated plot receives. Finally, it provides a backup disposal method should problems arise with the system in use. If there is no black water being generated, the two grey water tank outlets can lead to an irrigation system and a separate conventional drain field. This design affords the same benefits mentioned above. Other designs for grey water reuse and disposal, such as ponds for growing fish and/or algae and oxidation lagoons for total reten- tion and evaporation of the wastewater, are beyond the scope of this book. If you are interested in experimenting with these kinds of methods, check the library under Aquaculture. A typical grey