I know my shit thank you.
The nutrients that have been sitting in the water for a prolonged period will go stale and begin to produce micro organisms as they will feed on the nutrients themselves. This bacteria will be put into the plants and cause a number of issues. Root rot, nute lockup and heaps of other things. This is only 1 possibility. Nutrient embedded water is like a heaven to Bacteria and micro organisms - this is only if the water is left for a pro-longed period. 24 hours is the standard rule of thumb.
This in a sense, make the water poisonous to the plant or plants as you're putting bacteria and potentially deadly organisms inside your babies.