Patent of the month: gravity-driven water purification

Materials World magazine
31 Mar 2017

Dr Jennifer Unsworth of intellectual property firm Withers & Rogers describes an innovative water filter. 

There are many products that treat or filter water to remove contaminants and provide clean, drinkable water. One example is the LifeStraw, a straw-like device that allows the user to drink directly from a potentially contaminated source. It incorporates hollow fibre filtration technology to remove bacteria and other undesirable contaminants as water passes through the straw, resulting in clean water being consumed.  

LifeStraw SA, the Swiss company behind the invention has developed a range of products, one of which is the LifeStraw Mission. The Mission allows a user to filter water from a container with a capacity of up to 12 litres. The user fills the container with water, which passes from the container, through a pre-filter located at the base, and down a length of tubing to a filtration cartridge, the tubing being coupled to the container via a quick connector. The filtration cartridge incorporates hollow fibre technology, which filters the water to provide clean drinking water without the need for any chemical treatment. 

Some of the advantageous features associated with the LifeStraw Mission form the basis of a recently granted patent, GB2531177. For example, the patent describes that the porosity of the pre-filter provided in the container is selected from the interval of 10–120μm to ensure a high-flow rate, while preventing sand and other such particles from entering the hollow fibre filter. This is coupled with a useful configuration of the pre-filter within the container, which defines a space at the base of the container where impurities can be collected, preventing the pre-filter from clogging. 

From the pre-filter, water passes down the tube to the filtration cartridge. The granted patent also describes that a suitable filtration cartridge includes a bundle of hollow antimicrobial fibre membranes, as described in an earlier international patent application, WO2008/110172.  

In a filtration cartridge, which is about 30mm in diameter and 250mm long (approximately the size of the LifeStraw), between 0.08–0.3m2 of active membrane surface area is provided. As one example, an ultra-filtration single bore hollow tube membrane with a 0.02μm porosity can be used, which is able to filter bacteria, parasites, viruses and inorganic particles bigger than the pore size.

While both products feature hollow fibre filtration technology, the LifeStraw Mission offers a number of new features. The granting of this new British patent serves as a reminder that, although a new product may incorporate some of the same technology as an existing product, it may still be possible to obtain patent protection for new and inventive features. The refinements made to the existing technology may seem minor by comparison to the original invention, but if they deliver a new advantage in their own right then patent protection can be still be sought. The importance of protecting follow-on inventions and developments should not be underestimated. 

To view the patent in full, visit (PDF)