Yes it does flush out excess water that has been stored for however long it's been in your body. You may notice a significant weight drop just by drinking water alone.
People don't realise the impact salt has on body weight.
Here's some information from the NIH (National Institute's of Health) ...
RESULTS: Absolute and relative increases in drinking water were associated with significant loss of body weight and fat over time, independent of covariates (diet and exercise).
DISCUSSION: The results suggest that drinking water may promote weight loss in overweight dieting women.
Well i have completely stopped drinking Mt.Dew for 3 months now. The only fluids i take in are occasional milk, some apple juice, and about 2-3 gallons of water a day. I have lost about 25 pounds in 3 months.
I would say that drinking more water will surely help lose weight.
Drinking water helps fill you up and staying hydrated gives you more energy. Anything that helps you eat less or move more, will help you lose weight.