The question of whether to use tap water vs. bottled water to water plants depends in part on the plants you grow. Some very fragile plants may benefit from bottled water, although plants are much more likely to be damaged by watering practices, such as over watering or underwatering than by using tap water. Consider that in many rural areas, crops and yards are irrigated by untreated water from canals and ponds. These crops in general suffer no ill effects. According to the University of California Cooperative Extension, minerals added to tap water for human benefit pose no general threat to plants, however chlorinated pool water is harmful and should not be used.
In terms of cost, using tap water to irrigate plants is clearly the better choice. Bottled water can cost as much as 5 cents an ounce, while municipal water runs around 1 cent per gallon. Well water is often free, minus any yearly maintenance fees. Producing plastic bottles for bottled water uses more resources and shipping all those bottles uses gasoline.
Both bottled water and tap water are heavily regulated for acceptable levels of bacteria, coliform, lead and photon radioactivity, among other things. They are also regulated for acceptable color and odor. Tap water is regulated by the Environmental Protection Agency, while bottled water is classified as a food item and falls under the jurisdiction of the United States Food and Drug Administration. Since bottled water has a fairly good track record of safety, though, bottled water companies are low on the priority list for federal inspections, according to the FDA. Only bottled water crossing state lines is subject to federal inspections.
Chlorine and fluoride are added to municipal water, but according to the University of California, pose no threat to plants. However, sodium found in water softening systems may damage plants. Gardeners with water softeners should use outside taps to water plants, making sure those taps aren’t attached to the water softener. Well water is not regulated by any federal body, so homeowners are responsible for having their water tested regularly for safety. If well water isn’t safe for plant use, then it certainly isn’t safe for human consumption.
Bottled water is labeled under several different names, such as mineral water, artisan water and ground water. The two most popular brands of bottled water are nothing more than filtered tap water. Mineral water and distilled water are the only two types of bottled water that may have potential benefits or drawbacks that vary from those found in tap water. Mineral water, by law, must come from a geologically protected underground source and have a constant level of dissolved minerals in the water. These minerals, theoretically, might benefit plants, although providing good, amended soil would offer the same or greater benefits more economically. Distilled water has all minerals removed. This water is probably lacking in nutrients plants need. In both cases, tap water is usually the best choice.
Tap water is the clear winner for watering plants when it comes to environmental impact. The plastic used for bottled water takes hundreds of years to decompose in landfills, while tap water creates no landfill waste. When consumers use bottled water, they divert attention and resources away from the issue of maintaining safe and adequate municipal systems. This practice results in the commercialization of water systems.