Re: newbe question about freshwater tanks
How clean is the lake water? A filter will remove biological contaminants, but it won't remove hydrocarbons (fuel) or pesticides. I filter a lot of water from back-country ponds and lakes, but typically won't filter from large bodies of water with lots of motor traffic and runoff.
If the water is safe after filtering then I'd recommend a gravity filter (MSR and Platypus make good ones). They will filter about a gallon of water in 5 minutes with no work on your part. A pump style backpacking filter is slightly smaller but will filter a gallon of water with 5 minutes of continuous pumping.
boats that I sail on regularly: Pearson 28-2, Rondar 505, Yankee 30, Blanchard Junior