T'filat Tal (Blessing/Prayer for Dew) is a beautiful Jewish prayer that is said only once a year, on the first day of Passover (the morning after Leyl HaSeder). From this point on, the daily prayer for rain is replaced with prayer for dew.
First of all, keep in mind that the seasonality of rain versus dew is entirely based on the agricultural needs in the Holy Land - where the rainfall is crucial for livelihood of both people and livestock. Also, in the Omer season (the wheat harvest season - from Passover to Shavuot), it would be a curse to have rain falling as it would spoil the wheat harvest, which needs to dry completely in order to be harvested and stored properly. So any precipitation from Passover till Shmini Atzeret (the last day of Sukkot) needs to be gentle and mild.
According to this article about the Tfilat Tal, dew is the water that the heaven provides as a blessing of abundance to the plant life. Therefore absence of dew is considered drought, and a curse. This is demonstrated by the fact that the valley of Harod (near the Gilboa in Israel) has little dew. This is the mountain upon which King Saul and his son Yehonata have lost their lives. In his mourning, King David has cursed this mountain to not receive neither rain nor dew (Samuel II, 1:21).
As for the scent of dew - in my mind I associate it with nectar, tiny flowers, green tender leaves and all delicate things. Dew is what gives a garden in the morning its enticing, fresh and crisp yet delicate scent. In all my years collecting answers from readers and customers to what their favourite scents are, this "garden in the morning" is one of the most high ranking answers.
Dew takes its scent primarily from the plants it lands on. Tomato leaves will give it a funky odour, while sweet scented flowers will give it the taste of nectar. So it's really as versatile as all water: what it touches will transform it.
From my own existing creations, Bon Zai to me is a fragrance that captures the pure, tranquil feeling of early morning dew on pine needles and blades of grass. Likewise, many aquatic scents bring to mind dew, for example: l'Eau d'Issey. But neither are exactly dedicated to the concept of dew. In my early days in perfumery, I created a perfume called Coeli, which was first inspired by the dew on the herb garden in summer, which at this season was abundant with lush lemon verbena, melissa and lemongrass. It was obviously very citrusy at first. I later changed the scent into something entirely different, but still rather dewy. It did not fair very well, because I suppose it was not the bold, retro type of fragrance that my customers seem to be most fond of. It was far more modern woody-aquatic-floral type of scent. In the least few years I've worked on a scent inspired by Harbour Green Park (in Coal Harbour) - the scent of the dew-covered grass in the morning mingled with jet fuel and salty low-tide. Another scent that was also inspired by he same lemony herb garden was titled Clil (the name of my home village) but also had hay in it, which gave it a more bold presence. Perhaps it's time to go back to the drawing board with this scent and re-create my herbal tea garden once more.