It depends on the quality and contents of your water supply, as well as the environment that the water is stored in - did you leave it sealed in a bucket, open in a utility room or a filthy garage?
If you are leaving solutions out you will need to keep it bubbling to orevent anaerobic bacteria buildup and pH it every time you water (not the whole reservoir, just the amount you are going to use for that particular watering). After a few days it might be a bit gross so sling it. If you arent aerating dont keep for more than a day or two if you can help it.