I'm off to canada for three weeks and the end of June, and I'm planning to do some 3-4 day trails in the rockies.

The guide books all state that Giardia is a problem and that any water taken from a stream should be filtered before drinking.

The Pre-Mac Pocket Travel Well is cheap and lightweight - but I'm worried it'll take forever to filter the water (there's two of us going, so we'll need to filter around 6-10 litres a day)

A low weight is more important to me than the cost. I understand some filters have problems with clogging up.

Has anyone out there got any experiance? What do you suggest?

I have used the premac. It's slow. Very slow. It also has a limited capacity (50L?) and new cartridges are expensive. But it is light. For one person it was doable.

I also have a sweetwater guardian (very good flow rate, reliable, 500L+ capacity) and a katadyn mini (low-medium flow, lightest proper filter).

Alternatively if weight is the main concern then katadyn mp-1 tablets will kill giardia (and I think are the only thing recognised by the US EPA to kill crypto and giardia). However they take 30mins-4hrs to work (as will any chemical treatment for cysts) which tends to mean you have to carry a bit more water with you and negates the weight advantage.

If you're hiking around banff/lake louise, the sawback trail between the two (75km) is beautiful and very quiet.