noun
stagnant water; standing water
Water that has collected and remains still, often in a depression or container, and may become stale.
庭に溜まり水ができて、蚊が発生した。
Stagnant water formed in the garden, and mosquitoes bred.
古いバケツに溜まり水がたまっている。
Stagnant water has collected in the old bucket.
Refers to a puddle, often temporary and on the ground, while 溜まり水 emphasizes the water itself being stagnant.
Compound of 溜まり (noun form of verb 溜まる 'to accumulate') and 水 (water).