The employment of more than one thermosiphon solar water-heating unit may often arise in an application when considerable hot water requirements exist. The significance of the type of interconnection between these units on the thermal performance of the resulting system is addressed by examining a number of alternative coupling cases. For optimal performance, the overall system configuration in such cases should comply with the following criteria : (i) promotion of high temperature stratification within and between the storage tanks; and (ii) quick transfer of high-grade thermal energy to the user. Experimental results, obtained for three particular system configurations, agree well with predictions from the theoretical analysis.