This publication provides introductory technical guidance for mechanical engineers and other professional engineers and construction managers in design and construction of solar water heating systems. Here is what is discussed: 1. INTRODUCTION 2. SOLAR ENERGY APPLICATIONS 3. BASIC MATERIAL CONSIDERATIONS IN SOLAR ENERGY SYSTEMS. 4. COLLECTOR SUB-SYSTEM 5. STORAGE SUB-SYSTEM 6. TRANSPORT SUB-SYSTEM 7. CONTROL SUB-SYSTEM 8. SOLAR ENERGY SYSTEM PERFORMANCE 9. SUMMARY.