Finally I found a good test report from a Dutch boat-magazine. They did three test rounds: one with clean water left for two weeks in tanks in the sun. To test water with lots of bacterias the second test-round they used water from the Amsterdam-canals (don't drink that unfiltered(!). The third test they did with clean water after two weeks not using the filters (to see if bacterias grow in the filters and contaminate the water). The test where done bij C-lab (an independent lab). They only tested on bacterias like legionella, e-coli and salmonella because there starting point was clean water (without pollutions like chemicals or metals).

The "seagull IV" (in Spain sold by purewater spain) was a poor performer, referenced as not to be trusted for cleaning up bacterias. They also tested another system from the same manufacterer: the "Nature Pure" wich was perfoming much better. It couldn't filter the water to the Dutch drinkingwater norm level but the result was pretty close. The best system was 2Bsure. This system uses electrolyse to convert the minerals in water to chloride(!). In the end they concluded the best thing you can do is use chlorine (ordinairy tablets, bleach or with an expensive electrolise-system) and combine this with a coal-filter to remove the chlorine again to get a better taste.

For the Dutch readers: http://www.brightspark.nl/uploads/brochures/zeilen_2bsure_nl.pdf