A solar water heater is a system that harnesses solar energy to heat water for domestic, commercial, or industrial use. It typically consists of solar collectors, a storage tank, and a circulation system. 

**Types:** 
1. **Active Systems:** Use pumps and controls to circulate water through the collectors. These can be further divided into direct and indirect circulation systems.
2. **Passive Systems:** Rely on natural convection to move water through the system without mechanical assistance. These are generally simpler and more cost-effective.

**Components:**
- **Solar Collectors:** Usually mounted on rooftops, these panels absorb sunlight and convert it into heat.
- **Storage Tank:** Holds the heated water until needed, often insulated to minimize heat loss.
- **Circulation System:** Moves water between the collectors and the storage tank.

**Benefits:**
- **Energy Efficiency:** Reduces reliance on fossil fuels and lowers energy bills.
- **Environmentally Friendly:** Lowers greenhouse gas emissions by utilizing renewable energy sources.
- **Long Lifespan:** Solar water heaters typically have low maintenance costs and a long service life.

**Applications:**
- Residential heating (for baths and domestic hot water)
- Commercial uses (hotels, restaurants, and pools)
- Industrial processes (for washing and cleaning)

Overall, solar water heaters are a sustainable and efficient way to provide hot water, contributing to energy savings and environmental preservation.