Rainwater or Tap Water: Which is Best for Plants?

By Michael Jenkins

Water is important for plants—too much or too little can have disastrous results, and a consistent, effective watering schedule is a must for plant health. For outdoor gardens in particular, the question arises about whether rainwater or tap water is better for plants. This is a complex question, for reasons we'll explore over the course of this article. So let’s dig in and learn a bit more about tap water, rainwater, and how they both interact with your plants and soil!

Rainwater For Your Plants

We’ll start with rainwater, because the entire water cycle starts with rainwater. Rainwater is just that—the water that falls from the sky as rain (or snow or sleet or whatever other form of precipitation). Most plants have evolved to gather water from rain via the soil in which they grow. And rainwater brings some huge advantages when it comes to watering your garden. Rain is free, and in some places quite abundant. Rain can help introduce atmospheric nitrogen into your soil, which may help plants grow. In many places rainwater is relatively clean and pure, free of chemical additives that may interfere with soil chemistry or the growth of healthy microbes. And since rainwater is free, many gardeners can collect it fairly easily via the gutter system on their residence and a simple-to-use rain barrel system. Rain barrels are fairly easy to install and maintain, and we absolutely encourage you to learn more about them and if possible use them in your own garden.

So is rainwater a perfect choice, no-strings-attached? Well, sort of—there are some potential disadvantages to relying on rainwater for your garden. Rainwater is probably better for most plants, but rain doesn’t appear on demand. And while we can store rainwater in rain barrels or cisterns, this can provide a fertile breeding ground for mosquitoes and other disease-carrying pests if we don’t take steps to prevent this. Storing rainwater also requires both a way to collect it and the space and means to store it, which may be a bit difficult for apartment dwellers or folks with smaller gardening spaces. And finally working with stored rainwater means finding a way to move it to your plans, which generally involves multiple trips with watering cans or other portable containers. Some gardeners really enjoy this time in their garden space, others prefer a more convenient approach, so your own needs should be considered when choosing a rain water solution.

So what’s the alternative? Let’s take a good look at tap water and how it affects your plants . . .

Tap Water For Garden Plants

Tap water is exactly what it sounds like—the water that comes out of your home’s water supply when you turn a faucet or tap. It’s safe to drink in almost all of the US and Canada, and by extension is absolutely safe to use on most plants—some particularly delicate exotics have other needs, but that’s a subject for a different blog. With a simple garden hose, you can direct tap water where you need it, whenever you want it. This makes watering plants of all sorts relatively simple and easy, and can save a lot of time and effort in the garden.

As with all things, however, there are some downsides to tap water. Tap water comes at a cost. This is both monetary—tap water costs money in the form of your water bill—and environmental—tap water requires processing to make it safe to drink, which in turn uses energy and resources. Whether these costs are significant to you, your garden, and your community depends on your individual situation and location, but they’re something to be aware of. The chemistry of tap water is also different from that of rainwater. Tap water may contain chlorine and other preservatives to keep it free of microbes. While that’s good for health and safety, those same chemicals may not be great for your soil health. This can be ameliorated by filling containers with tap water and leaving them open to the air for a few hours so the chlorine can evaporate away, but again it’s something to consider. The pH of tap water is likewise different from rainwater. While rainwater tends to be neutral to slightly acidic, tap water tends to be slightly alkaline. As some plants prefer acidic soil conditions and others prefer alkaline soil conditions. As with the costs of tap water and its impact on soil life, this is just another factor to keep in mind while making these decisions.

Water Your Garden

Both tap water and rain water have gardening pros and cons. Which one is right for you—well that depends on your garden space, your personal needs, and the climate in which you live. The important thing for us is that you have the information you need to make the right choices for your garden and develop flexible, effective methods of watering that keep both you and your plants happy. So, whether you’re watering with rain water or with tap water, get out there, spend some time in the garden, and show your plants some love.