If you have a microscope and you place pollen on a slide in some water you can see that the pollen absorbs too much of the water and bursts. Of course, the pollen does not burst when it is placed on a stigma that is wet with its fluid (stigmatic fluid). That fluid is special and has perhaps fats or oils, sugars and other compounds that are specially for the pollen so that instead of bursting, the pollen grains germinate and develop a pollen tube that enters the style and grows down to the ovary, etc.
Now we come to my speculation.
As pollen that is placed in ordinary water bursts the material inside the pollen grain becomes mixed with the water. That material contains sugars, proteins, fats, and other compounds. If there is lots of pollen and little water then as the pollen grains burst the ordinary water may become more like the stigmatic fluid (or more like artificial pollen medium). The most important part (in terms of bursting or killing the pollen) is the amount of sugar in the water (5% to 10% is probably enough to stop pollen from bursting). So it may be possible that as more and more pollen grains burst the water (when there is only a very little) becomes less and less able to make the pollen grains burst and some pollen may survive.
I would suggest trying the pollen, especially if after a light rain and the pollen has dried it looks and acts fluffy (or normal).
