This is an extremely difficult question in which to place an exact dollar value or general percentage price differential. One can do a historical analysis, but there are several reasons why this may be flawed: 1) What exactly is the definition of "waterfront" in a previous listing; 2) there are not enough sales of otherwise-comparable properties during the same time period in an area or community to make an accurate call on this; 3) people who have waterfront generally also make more internal improvements in a home which would not get noted in a typical "CMA"(competitive market analysis).
This is much more an art than a science, or a mathematical question subject to easy analysis. If you have a home on one of the lakes with dramtic and sweeping views, your home will have SIGNIFICANTLY more value than neighboring properties without such views. In fact, the other homes may linger on the market even if listed at a price so far below that of a recent lake front sale for one simple reason: a large percentage of buyers do not want to compromise. They want lake front, and probably excellent lake front views.
Here is a current example: There are two t/h's in Harbor Court currently listed which are having a difficult time selling because they are not on the lake (they do have lake priveledges). These same models would have easily cleared the market at 20%+ higher if they were positioned, as many in the community are, with a stunning view of Lake Thoreau. In the current tight supply/denad environment, lake front sells almost immediately. Another community with simple comparison is Lakeport: homes on the water there sell at 25%+ premiums to their peers just 100 feet away, but on the inside w/o lake view. And if a lake front home hits the market, it usually sells in days. To me, this implies that residents are actually understating how dramatic the difference is, and selling too low.
One last point, and I apologize for being so verbose, be careful of what people call "lake front". There is a huge difference between having a view on one of the fingers of a lake, with some views but simply not panoramic lake views. Others will promote "lake front" or imply by saying "lake views"if they have a sliver of a view from the balcony and little else in terms of views. Such properties should not carry much premium at all.
In summary, a pure lake front view in an excellent community will yield a huge proce differential in most cases(25% +). And it should be that way.
There are times when "looking at the comps" is not going to yield you the accurate answer you need. In fact, in most neighborhoods, "looking at the comps" can yield some dangerously incorrect conclusions (a basic question: define for me "the comps"). But your waterfront in Reston question requires on-the-ground intelligence from people who know this market. Feel free to call me at 703-855-7299 or email at firstname.lastname@example.org.
Ray gives sound advice and I commend him for that. I have sold water front on Lake Anne and I am familiar with pricing. There is more impact based on the view and the price point of the home. This is a unique feature and can be hard to put a number on. It will also matter if there is a dock, possibility of a dock, degree of view and where the view is from. Ex. a great view from a bedroom window..will not be as valuable as a great view from say the deck. I don't want to overemphasize the obvious..but you know how folks can exaggerate! If you would like some help on pricing etc. feel free to contact me. My office is at Wiehle and Sunrise.
Erik J. Weisskopf, ABR,CDPE,CRS,GRI
The demand for the community and the neighborhood comes into play, too.
I am happy to further analyze this, but more information would be required to provide a fair and balanced answer.