In most cases tap water will work just fine in your AeroGarden, there are exceptions to this rule. Depending on where you are located in the world some tap water may be harder than the recommended amount. The hardness of the tap water refers to how many minerals have been dissolved. For example, some tap water comes from man made wells which result in hard tap water exceeding 600 parts per million of total dissolved solvents (PPM). In this case your water will be unacceptable for your plants to flourish in the AeroGarden. If you are unsure of the quality of your water a PPM meter can be purchased for under $10. This device will tell you straight away if your water is high in total dissolved solvents (over 400 PPM). If you are certain that you do not use well water and are receiving tap water from your municipality then there is a good chance your water is below this cap for total dissolved solvents. Some municipalities even publish this information online for resident’s that are keen to know more.