Reverse osmosis (RO) is one of the main technologies used to desalinate brackish water and seawater. Here are the main reasons why it tends to be expensive:

Pre-treatment: Reverse osmosis (RO) requires extensive pre-treatment of the feed water, including screening, filtration, dechlorination, and other processes. These pre-treatment steps incur additional infrastructure costs, as specialized equipment and facilities are needed to prepare the water before it undergoes the RO process.

Membrane replacement: The membranes used in RO systems are expensive and have a limited lifespan. Periodic replacement of these membranes is necessary to maintain the system’s efficiency and effectiveness. These replacements add recurring capital costs to the operation of RO plants.

 Disposal of concentrates: The remaining salt concentrate from the RO process requires additional processing before it can be safely disposed of, as its discharge can potentially harm the environment. This necessitates further investment in infrastructure and operational costs to manage the disposal process effectively.

Durability: Constructing RO systems resilient enough to endure high water salinity levels often involves the use of specialized metals and plastics, which can be more costly. Ensuring durability adds to the initial construction expenses of the systems.

Land and labor: Securing coastal land suitable for constructing large RO plants typically comes with higher real estate costs. Additionally, if skilled labor needs to be imported for the project, wages may increase, contributing to overall project costs.

In summary, while reverse osmosis (RO) technology delivers high-purity water through fine membrane filtration, it comes with substantial costs associated with energy, materials, construction, and concentrate disposal. This makes it a comparatively expensive option when compared to utilizing natural freshwater resources. However, as technology advances, costs are gradually decreasing, making RO a more economically viable solution over time.