Like rainy seasons, winter also contributes to the supply of groundwater sources. However, no matter how pristine snow may seem, meltwater, or melted snow, may not necessarily contribute to cleaner groundwater sources.
During dry season, as water level drops, previously submerged soil layers come into contact with air which is always found between crumbs of soil. The oxygen in this air reacts with substances found in the soil, and some of them dissolve and seep into the groundwater. This chain of events may also be affected by soil microbes.
On the other hand, problems may also be caused if the groundwater level rises from meltwater or during rainy days. Groundwater starts flowing through soil layers that were previously above its surface and that may contain harmful substances.