Reading: きくすい げつ ざいしゅ, or more Japanese: 水を掬すれば、月 手に在り
there's a sister scroll to it that completes the poem: 弄花香滿衣 (ろうか こう まんい or 花を弄つ) (you play with flowers, their fragrance fills your sleeves).
Not really a 禅語, it comes from Chinese poetry and is more about the complete immersion in nature