At Forest Fundamentals, we have been long-term users of the old British Forces Millbank bags. However, these bags are extremely hard to find now, and the ones we did manage to get our hands on showed signs of years of use - they were full of stains and oil residue. So we thought, why not start to make our own!

Meet the Forest Fundamentals Millbank Bag! We have used similar proportions as the original British forces bags. However, after some testing, we made a few design changes including:

The materials: The bags are handmade using a high-density 12oz unbleached Cotton canvas. Unbleached Cotton canvas is made from natural cotton fibers and has not been subjected to the chemical bleaching process. For additional strength and durability, we have used V69 3ply Bonded Polyester Thread. The same thread is used in high-quality tents and backpacks.

Overlock double switching has been used on all of the seams for added strength and to avoid any raw edges. The overlock stitching also provides another layer of filtering. Our Millbank bag is larger than other designs, making it possible to purify larger amounts of water at once. We print the instructions and logo onto the bag using waterproof, non-toxic dye so there is no chance of it washing off after use

The Millbank also comes with a 1M long 550lb ‘Survival Cord’ lanyard which includes strands of copper wire, fishing line, waxed jute, and parachute cord. This multi-purpose card is invaluable in the field and has a range of uses including repairing shoelaces, fishing, snares, shelter building, and more. The super-long lanyard also makes it possible to hang the bag close to the collection device, avoiding any possible spillage caused by the bag swaying in strong winds.

Also included is a 210D Nylon waterproof drawstring carrying bag and a detailed instructions card. The pouch makes it possible to transport the bag after use without soaking the inside of your pack! Strapping the Millbank bag to the outside of your pack is a great way to dry the bag on the move. The carrying bag also doubles as a great emergency tinder pouch!

During our testing, we explored different bag shapes and materials to boost the filtration rate while ensuring complete detritus removal from the water. We found that expanding the filtration point quickened the process. Subsequent assessments with turbidity meters revealed that this faster filtration did not compromise the bag's ability to filter out detritus, provided the material of the bags was kept the same.

What is a Millbank Bag?

A Millbank Bag is a highly effective water filtration device designed to remove detritus from water. These detritus include sand, mud, silt, or other suspended particulate matter.

Ensuring the removal of all detritus from the water before proceeding with further sanitation is of the utmost importance. Even in the absence of waterborne diseases, turbid water can still cause irritation and harm to the digestive system. Moreover, turbidity negatively impacts the effectiveness and lifespan of other water sanitation systems including the well-known LifeStraw, for instance. Prioritizing the filtration of impurities is crucial for obtaining safe and clean drinking water.

It’s essential to note that a Millbank bag will not effectively filter out pathogenic organisms unless they are attached to the detritus being filtered. Additional sanitation methods, such as chemical or heat sterilization are required to ensure the water’s safety. If your water source is already clear and free from detritus, using the Millbank bag may not offer significant advantages. However, few of us are lucky enough to find such pristine water sources in the wilderness! Hence, the Millbank bag still remains a fundamental part of any outdoors person’s water purification systems.