It is not a bad idea to keep about a 10 gal trash can sized container outside to collect rainwater for your crops. You can cover the water, if you like, on non-rain days in order to try to keep mosquitos from laying their eggs in it… which… would not hurt the crops so much, but… seems generally ideal to keep pests out of it.
If you are using it every three days, as is about the right amount, you won’t have any standing water issues, anyway. But, it doesn’t hurt to keep the mosquito nests to a minimum, am I right?
This water is great for crops, as one can imagine. It has none of the city treatment contaminants in it, and is mineral-rich… and… it’s free. You can scoop a bunch out with a watering can, in order to spread it evenly and gently over your darling growing carrots.