Baruch Hashem, as I type these words, it is pouring outside. The Israeli countryside, from North to South, is enjoying The Almighty’s cherished gift of rain.
In the beginning, there was no rain. Only during the second segment of that singular week, that period which was composed of seven inscrutable days, did Hashem separate the heavenly waters from the waters below. Before that, He fashioned space, time and light. That is, the vessels for the waters of the upper chamber were made before those exalted waters, themselves, came into being.
Neither flora nor fauna were created before rain existed. Specifically, dry land and plants were brought into existence on Day Three, sea creatures and birds were brought into existence on Day Five, and land animals and humanity were brought into existence on Day Six. From the inauguration of existence, onward, it has been made apparent that life needs water to carry on.
Accordingly, when we pray for rain, we implicitly pray, as well, for the life giving water that fosters our fruit trees and fields, for the heavenly kisses that green our livestock’s pastures, and for the precious liquid that elevates the waterways where our fish breed. We ask for rain since birds rely on that precipitation, as do animals, and as do we.
Rabbi Yoseph Y. Jacobson writes in “Souls in the Rain,” “[w]hat is rain? In the midst of intimacy between heaven and earth, procreative drops from heaven are absorbed, fertilized and nurtured by mother-earth, which in time will give birth to its botanical children.” In short, no rain means no life. No heavenly water means no Earthly survival.
Some mystics point out that the quality of rain depends on the quality, i.e. on the relative goodness, of our actions. In requesting heavenly waters, we evoke the merit of almost all of the Ushpizin; of the Avot, of Moshe, of Aaron, and of Yoseph (as Yoseph is represented through the twelve tribes, more exactingly as he is represented through his sons and his brothers, exclusive of Levy). Rabbi Joel Padowitz explains in “The 7 Ushpizin Guests,” that “Abraham represents love and kindness, Isaac represents restraint and personal strength, Jacob represents beauty and truth, Moses represents eternality and dominance through Torah, Aaron represents empathy and receptivity to divine splendor, [and] Joseph represents holiness and the spiritual foundation.” In other words, we ask G-d to consider our merits and to reward us, in turn, with rain.
Other sages espouse that rain derives from supernal sources and is of various types. Some types of water, for instance, is good for trees, whereas other types of water is good for vegetables. Rabbi Nathan Schapira states in “The Rains of Israel” that some plants need “male waters,” i.e. rain, and that other green growth can get by with “female waters,” moisture from below, from seas, lakes and rivers.
Interestingly, “female waters” are sustained by “male waters.” When it rains, for instance, in the Upper Galilee and in the Golan Heights, the flow of the Jordan River increases. Subsequently, the water level of the Kinneret, Israel’s largest fresh water source, increases. As of this writing, that lake’s level is above the lower of the two red lines and is approaching, IYH, the upper red line.
When, in contrast, the Kinneret’s water level drops, we Israelis are forced to rely progressively more on desalinized water, on wastewater and on greywater. Desalinized water is often replete with bromides, with seawater compounds. Wastewater, i.e. sewage water, can contain blackwater (human waste), manufacturing liquids, chemical-laden agricultural drainage, and other undesirable components. As per greywater, Amit Gross, et. al. write in “Environmental Impact and Health Risks Associated with Greywater Irrigation: A Case Study,” that “greywater may be of similar [low] quality to wastewater in several parameters such as BOD and faecal coliforms. For some other variables such as boron and surfactants, greywater may even be of worse quality than wastewater.” Fresh water remains preferable to all available alternatives. Rain is needed to sustain us with fresh water
Not surprisingly, Torah, which is the source of life at a very profound level, is equated to water. We bessech Hashem to open our souls to Torah. We beseech Him to send us rain.
Gishmei Bracha, the Divine blessing of rain, of the wet nourishment that falls on the right place, and Geshamim B''itam, the Divine blessing of rain that falls at the tight time is what we request. 
This wet week in Israel, we slosh through puddles and transport ourselves slowly. This wet week in Israel, we are Blessed.