Spiral wound reverse osmosis is widely employed for the production of desalted water for municipal and industrial purposes.Ultrafiltration is gaining more and more significance as pretreatment, compared to "conventional" pretreatment (media filtration and cartridge filtration).Ultrafiltration is extremely suited for difficult feed waters since it provides an absolute barrier for suspended solids, silt and micro biology.Initially ultrafiltration membrane systems were designed to replace media filters, while maintaining an identical process lay out: pretreatment and reverse osmosis are decoupled by means of an intermediate buffer tank (non-inline systems).The presence of an intermediate buffer tank has several disadvantages: it increases weight and footprint and it adds extra equipment because transfer pumps are required.The main disadvantage however is the fact that the buffer tank provides a body of stagnant water that will provide a breeding ground for micro biology.Therefore the water elaving the buffer tank will be of less quality than the water entering the buffer tank.A new generation ultrafiltration systems uses a different set up.The feed water is kept pressurized from intake works up to the SWRO high pressure pumps: intermediate buffer tanks and pumping stations are eliminated.The UF filtrate pressure is sufficient to feed UF filtrate directly into the high pressure pumps.Typically the UF system still requires a backwash tank with backwash pump.This design is called semi inline: although being marketed as inline systems, these still require some form of water storage between UF and SWRO.The latest generation of ultrafiltration systems is the first system without any backwash tank.This new innovative design uses a completely different approach that eliminates all disadvantages.Multiple UF units are operated in parallel.The filtrate that is being produced is fed directly to the SWRO units.When a backwash is called for some of the filtrate is reversed through one of the UF units additional to the RO being fed.This completely eliminates all disadvantages associated with storing backwash water.The UF feed pumps are used for driving the backwash process.This new innovative design is called a true inline UF system.It combines the smallest footprint and weight of any SWRO pretreatment option with robust operation.This paper describes designs of semi inline systems and compares these to true inline systems.Based on these designs an assessment is made of the reduction in total cost of ownership of true inline SWRO plants.