Affordable and effective domestic wastewater treatment is crucial for public health, especially in developing countries with limited resources. This guide covers methods for designing low-cost, low-energy, and high-performance wastewater treatment systems that can be used for agriculture and aquaculture. The focus is on natural systems like waste stabilization ponds, constructed wetlands, and anaerobic reactors. The goal is to reduce wastewater-related diseases and environmental damage by producing safe effluents for reuse. This information is important for engineers, students, and anyone interested in sustainable technologies for wastewater treatment.