Here are the key components, how it works, types, advantages, and some challenges:

Key Components of an RO Plant

1. Feed Water Source — Could be surface water, groundwater, seawater, or treated wastewater.
2. Pre-Treatment Units — To protect the RO membrane and improve efficiency. Includes:
   • Multimedia or sand filters (to remove suspended solids). 
   • Activated carbon filters (to remove chlorine, organics, odour). 
3. • Water softeners or hardness removal (to prevent scaling). 
4. • Chemical dosing (antiscalants, pH adjustment, dechlorination). 
5. High-Pressure Pump — Pushes pretreated water through the RO membranes at sufficient pressure. 
6. RO Membrane & Pressure Vessels — The core filtration unit. The membrane is semi-permeable, letting water molecules pass, rejecting dissolved salts, microbes, etc. Pressure vessels (FRP or SS) hold the membrane modules
7. Energy Recovery Devices (in large systems) — To improve energy efficiency by reclaiming pressure or energy from the reject stream. 
8. Post-Treatment / Polishing — After the RO membrane, sometimes additional treatment (like UV sterilization, carbon polishing, or remineralization) to improve taste, ensure microbial safety, and adjust water quality as required. 
9. Instrumentation & Control Systems — Includes pressure gauges, flow meters, TDS/conductivity meters, switches, sometimes a PLC panel for automation
10. Storage Tanks — For both raw feed water and treated (product) water. Sometimes also for reject water before disposal

Working Principle / Steps

1. Pre-treatment to clean up large particles, remove chlorine, adjust hardness, etc. This protects RO membranes. 
2. Feed water pressurization by high-pressure pump. Pressure must exceed the natural osmotic pressure of the feed water for reverse osmosis to occur. 
3. Membrane separation: Water is forced through the membrane; clean water (permeate) passes through, while the contaminants are left behind and flushed off as waste (concentrate / reject). 
4. Post treatment if needed (e.g. for taste, microbial safety
5. Storage / Delivery of the purified water

Types of RO Plants

• Domestic / Residential – small capacity (e.g., few tens of liters per hour).
• Commercial – larger capacity for offices, hotels, schools, etc.
• Industrial – high capacity for factories, boiler feed, pharmaceuticals, food processing, etc.
• Seawater RO / Desalination – RO plants treating seawater which require higher pressures and more robust pre-treatment. 

Advantages

• Removes a wide spectrum of impurities: dissolved salts, heavy metals, pathogens, etc. 
• Produces safe drinking water, good for health.
• Can be scaled to required capacity.
• Commercial & residential RO plants reduce dependence on bottled water or unsafe sources.

Challenges / Limitations

• Energy requirement is significant, especially for high TDS water or seawater.
• Waste / reject water: RO produces a, sometimes large, volume of reject water that needs disposal.
• Maintenance: Membranes can get fouled or scaled; pre-treatment must be good; periodic cleaning needed.
• Cost: Capital cost for large plants, cost of consumables (membranes, chemicals, filters).