MSR Miniworks £54 from Sports Direct

[chris_r]

These usually go for £90 and are an excellent bit of kit. They weigh less than 1/2 a litre of water and are good to filter up to 2000 litres per cartridge. Two left in stock.

http://www.amazon.co.uk/dp/B0032GPI...ve=22134&creativeASIN=B0032GPIME&linkCode=asn

I recently picked one up and I love it. Screws directly to Nalgene bottles and Ortlieb water bags.

 

[GordonM]

I have one of these (purchased in the mid 90s) and it has served me well for many backpacking trips and outings. It is easy to maintain and field maintainable, as well. Good value for the service I have gotten from it.

Gordy

 

[Harvestman]

Another vote for these. Excellent bit of kit.