Filter for surface untreated water e.g. lake/river water

We are in the process of building a lake house, and we suspect that we may have difficulties in drilling a well and may be forced to pull water from the lake.
Do your "whole house" filtration systems work for these purposes? Also, what impact does a 6gpm flow vs a 12gpm flow have on how the water gets used in the house - is there less pressure, or what? Do we need a holding tank to store the filtered water or does the filtration occur upon usage? At this time we do not expect that the house will be occupied full time.

Our "whole house" water filters are designed for well and or city treated water. For surface untreated water e.g. lake/river water our commercial/light industrial water filters fitted with Doulton ceramic cartridges are often used as in your case.
No need for holding tank as the filtration occur on demand. Choosing the flow rate depends on the amount people occupying the house and amount of bathrooms, generally for vacation home 6-8 GPM not filtering the irrigation system is sufficient. The pressure have nothing to due with the flow rate and typically the pressure leaving the ceramic filters is 50% less than the inlet pressure e.g. 60 PSI in 30 PSI out on clean ceramics, they are tight therefore we recommend 1 micron nominal pre-filter (inexpensive) to reduce the cleaning frequency.
On the following link you can view our systems: http://www.doultonusa.com/commercial_industrial_filters/commercial_and_industrial_water_filters.htm