The main issues (assuming sealed container so no evaporation) with storing nute water is precipitation of nutes out of solution and combination of nute compounds. If given long enough various chemicals in solution will combine with others to form compounds the plant can't use or compounds that will solidify out of solution. This is one reason you don't see many liquid 1-part nutes because it is not a trivial task to make it stable and have a decent shelf life.
If you're using old nute water the first thing to check is if there are solids collecting in the bottom. If so, toss it out. However, the plant usable compounds may have split/combined with others to form compounds the plant can't use, so there is still a chance the water is bad.
If you're just storing for a week you're probably fine. If you want to pre-mix the nutes with water well in advance you can, just keep the nutes separate. For instance instead of adding 10 ml gro and 10 ml bloom to 1 gal water add them to separate 1/2 gal containers. Then use equal amounts of each of these dilutions at watering time. This way is more complicated (especially with lots of different nutes), so make sure you double check your math for watering amounts. If you're using dirt you still want to mix all the premixes together before watering, for hydro it doesn't matter since they'll mix in the reservoir.
Remember: If you're not part of the solution, you're part of the precipitate.