9 Liquids You Can Use To Water Your Plants (And 10 To Avoid)

This morning's coffee, pasta water, the dregs from your wine glass—find out which of these liquids are plant-friendly, and which aren't.

December 14, 2016
water on leaves
Kyle Szegedi/unsplash

Plants need fresh water—and sometimes a lot of it—to thrive. Unfortunately, fresh water is getting scarcer and more expensive in many areas of the planet. If water restrictions or drought have you wondering what else besides tap water you may be able to use for indoor and outdoor plants, we have some advice. Look beyond your faucet and hose; there are plenty of liquids that are just as good (or better) than tap water for watering plants. We've rounded up all the possibilities, along with the liquids you should never, ever use to water your plants.

(Whether you're starting your first garden or switching to organic, Rodale’s Basic Organic Gardening has all the answers and advice you need—get your copy today!)

rain water
Joy Stamp/unpslash
Liquids That Are Even Better Than Tap Water

Rainwater is the gold standard for watering plants since it's soft and low in salts and contaminants. But of course, rain doesn't always arrive when or where you need it. If you have access to a roof and a downspout, and a place to put a heavy barrel, consider installing a cistern or rain barrel to make the most of light rains and to store extra water for dry periods. (You can even install more than one.)

Cooking Water
The water you use to blanch or cook food is often rich in vitamins and minerals that can benefit plants. If you can’t use this water in a soup or other cooking projects, go ahead and use it for your plants. Just make sure to avoid watering plants with cooking water that contains more than a trace of salt, oil, sugar, or starch. And use the liquid as soon as it cools down so it won’t get nasty with bacteria.

Aquarium Water
When you clean out your freshwater aquarium, you can definitely use the nutrient-rich water for your plants. Just don’t even think about using water from a salt-water tank on plants.

Pond Water
Any fresh water source, such as an outdoor fishpond, lake, farm pond, or creek, is a great source of water for plants. Avoid water downstream of industrial pollution sources; if there are lots of living plants and/or animals in the water, it's probably safe.

Related: Is Your Tap Water Safe?

cup of tea
Morgan Sessions/unsplash
Liquids That Are Just As Good As Tap Water

Tap water isn’t perfect, but it’s what most of us have access to. If you have chlorinated water, allow it to sit in open containers for a day or so to allow the chlorine to escape into the air. Avoid using softened water.

“Allowed To Run” Tap Water
Water that goes down the drain while you wait for it to heat up or cool down, or the water that runs while you flush the pipes before drinking, is waiting to be harvested. Keep jugs or basins on hand to collect this water, which would otherwise disappear down the drain.

Gray Water
This is water that has been used to rinse or wash veggies or rice, hands, bodies, dishes, and clothing (except diapers). While sophisticated gray water recovery systems are a great idea, they're also costly and may require odious permit processes. Luckily, you can harvest a lot of grey water by washing your hands over a portable dishpan you set in the sink, rinsing food or dishes in the portable dishpan, or scooping rinse water out of sinks or tubs into a bucket.

Caution: Some soaps, detergents, and cleaning products contain high levels of salts or other compounds that make them harmful to plants. (The California-based Ecology Center has a good list of gray water-compatible products, as well as ingredients to avoid.) Rinse water tends to be cleaner than wash water. If you use completely biodegradable products, you can collect/scoop out water to use for watering plants.

Dehumidifier Water
If you run an electric dehumidifier, the condensate is reasonably pure water. Periodically scrub out the collection container to prevent microbes from setting up camp.

Tea, Unsweetened
Both regular and herbal tea tends to be reasonably neutral (neither acidic or alkaline) so go ahead and use the dregs of your cup on your plants. Adding lemon, sweetener, or milk will make your tea less desirable for watering purposes.

Melted ice is just water, and perfect for plants. Let it melt first or place ice cubes on the surface of the soil, not touching the plant.

Related: Top 10 Ways To Save Water In Your Garden

Kyle Meck/unsplash
Liquids That Are Worse Than Tap Water

These are OK to use once in a while, especially when diluted with water, but don’t use them exclusively.

Leftover Coffee
Coffee tends to be moderately acidic (its pH is 5.5, where neutral is 7 and vinegar is 2.4). Caution: avoid coffee with more than a trace of sweeteners or creamers.

Leftover Seltzer
Fresh bubbly seltzer is very acidic—forcing the carbon dioxide into the water makes it form carbonic acid. Flat seltzer is only moderately acidic since some of the acid has escaped. Caution: some seltzers can be rather high in salt, so don't use those to water plants. 

cup of milk
baby qb/unsplash
Liquids You Should Never, Ever Use To Water Your Plants

Plants do best when the soil is in the neutral range, so adding liquids that are either very acidic or very alkaline is a bad idea and can lead to mineral imbalances and plant death. Plants can’t use sugars, starches, or proteins directly, and while the microorganisms in the soil (mostly outdoors) can, they can only handle small amounts. Even worse, however, is that liquids with high sugar and/or salt levels can actually pull water out of plant roots rather than allowing water to be absorbed. You also want to avoid liquids containing most cleaning products, sanitizers, or other toxic chemicals.

Leftover Or Soured Milk
Milk is neutral, but it is rich in sugars, proteins, and fats, and thus isn’t a good choice for watering plants. (Try these 7 ways to use up leftover milk instead.)

Soda, Juice, Or Sports Drinks
Most soft drinks and juices are both very acidic and very sugary—two reasons to not use them to water plants unless they are very diluted. And while they are only acidic, rather than sugary, also avoid using artificially sweetened diet drinks to water plants.

Pickle, Olive, Or Sauerkraut Juice
Vinegar is very, very acidic and the vinegar-based juice left behind in the jars of vinegar-based products is still very acidic, and sometimes quite sugary too. Juice from fermented pickles and sauerkraut is very acidic and salty. None of them are good choices for plants. Juice from naturally fermented products is loaded with beneficial bacteria however, so you may want to find ways to consume it yourself. (Here's how to make your own sauerkraut in a jar.)

Leftover Beer Or Wine
Beer and wine are both very acidic and not suitable for watering plants. If you hate to waste it, use leftovers in cooking or to make your own vinegar. (Here are 10 more things you can do with leftover beer.)

Swimming Pool Water
There's just too much chlorine and other chemicals designed to stop algae and bacteria from growing in the pool to make this liquid a good choice for plants. The exception would be if you have a “natural” pool with a biological filter system, in which case the water is great for plants.

Sea Water
This water has too much salt for watering anything but plants native to the dunes or salt marshes by the seashore.

Urine is very high in valuable nutrients, but you need to think of it as concentrated liquid fertilizer, not water. Caution: Straight urine kills plants and, even diluted with 5 to 10 parts of water, the salts may build up in potting soil or outdoor garden soil in climates that don’t get heavy rain at least a few times a year.

Black Water
Water that has been used to flush toilets or to wash diapers or other things that have been heavily contaminated with fecal mater is called black water. It isn’t suitable for watering plants without extensive treatment; there's just too much chance of spreading bacteria that could make you sick.