In certain populations, drinking a glass of water 30 minutes before your meal can have a positive effect on health. These studies didn't consider mineral water (but others may have).
In 2007, Walleghen et al. found that pre-meal water consumption reduces meal energy intake in older subjects, but not in younger subjects. (Walleghen 2007)
Whether or not this decrease in energy intake is a "positive effect on health" is a different question, not addressed by the study. They suggest one circumstance that it could be considered a positive effect on health: "older adults, [that] are at increased risk for overweight and obesity". However, they also say that "intervention studies are needed to determine whether pre-meal water consumption is an effective long-term weight management strategy for the aging population". (Walleghen 2007)
In 2008, Davy et al. repeated this study, but focussing on overweight and obese older adults. (Davy 2008) They found that "meal energy intake was significantly less in the water preload condition as compared with the no-preload condition". (Davy 2008) Like Walleghen et al, they also say that "given the high prevalence of overweight and obesity among older adults, future studies should determine whether premeal water consumption is an effective long-term weight control strategy for older adults". (Davy 2008)
Dennis et al. performed a longer term study in 2010. (Dennis 2010) They found that pre-meal water consumption increases weight loss during a hypocaloric diet intervention in middle-aged and older adults. (Dennis 2010) Regarding the health benefit of this result, they say that "identifying successful weight management strategies for middle-aged and older adults has significant public health implications". (Dennis 2010)
Son et al. recommend drinking water before a meal in elderly people who suffer postprandial hypotension (after-eating low blood pressure). (Son 2010)
Daniels, M. C., & Popkin, B. M. (2010). Impact of water intake on energy intake and weight status: a systematic review. Nutrition reviews, 68(9), 505-521.
Davy, B. M., Dennis, E. A., Dengo, A. L., Wilson, K. L., & Davy, K. P. (2008). Water consumption reduces energy intake at a breakfast meal in obese older adults. Journal of the American Dietetic Association, 108(7), 1236-1239.
Dennis, E. A., Dengo, A. L., Comber, D. L., Flack, K. D., Savla, J., Davy, K. P., & Davy, B. M. (2010). Water Consumption Increases Weight Loss During a Hypocaloric Diet Intervention in Middle‐aged and Older Adults. Obesity, 18(2), 300-307.
Son, J. T., & Lee, E. (2010). Effect of Water Drinking on the Postprandial Fall of Blood Pressure in the Elderly. Journal of Korean Academy of Fundamentals of Nursing, 17(3), 304-313.
Walleghen, E. L., Orr, J. S., Gentile, C. L., & Davy, B. M. (2007). Pre‐meal Water Consumption Reduces Meal Energy Intake in Older but Not Younger Subjects. Obesity, 15(1), 93-99.