וְהָאָ֗רֶץ אֲשֶׁ֨ר אַתֶּ֜ם עֹבְרִ֥ים שָׁ֙מָּה֙ לְרִשְׁתָּ֔הּ אֶ֥רֶץ הָרִ֖ים וּבְקָעֹ֑ת לִמְטַ֥ר הַשָּׁמַ֖יִם תִּשְׁתֶּה־מָּֽיִם׃
但你們要過去得為業的那地，是有山有谷之地，是靠天上的雨水來滋潤的。
Sefer HaMiddot
4. Recital of Tehillim (Psalms) is a segulahfor rainfall. [The letters of the word] Tehillim [are the acronym for the Biblical phrase] -- "According to the Rains of the Heavens, You will drink Water."
Sefer HaMiddot
7. The saying of Tehilim (Psalms) is conducive (segula) to causing rain to fall. [This is learned from the Hebrew letters of the word] TeHiLiM= Limtar''H'ashamayim'T'ishteh'M'ayim (Deutronomy 11:11 "According to the rain from heaven, you will drink water.")