Let's invent a proverb: it's an ill snow that melts no good.

According to the Interior Department's Geological Survey at Reston, which doubtless had numerous no-shows among its workers on the day of the infamous Feb. 11 snowfall, the meltdown did a lot of good toward restoring the depleted flow of the Potomac River and the ground-water levels of the region's soil.

As the snow melted, the survey recorded a flow rate of 6 1/2 billion gallons a day at Little Falls. The good news is that was nearly twice the pre-snowstorm rate. The bad news is that the flow remains about 35 percent below normal for this time of year.

For ground water, an important index for farmers and backyard gardeners, the survey reported a rise of seven inches since January in the level of its "key index well" at Fairland, in northeastern Montgomery County. It rose about eight inches as a direct result of the snowfall.

Survey hydrologist Myron Lys said the rule of thumb is that 10 inches of snow equals one inch of rainfall, although large-flake snow tends to have higher water content and dry powdery snow, less.

"Since the Potomac Washington area received 16 to 24 inches of snow two weeks ago , that amounts to a two-inch rain or more. However, the water . . . was released slowly each day in the form of snow-melt runoff, providing daily feedings to surface and ground water sources.