Water is one of the most important things when it comes to life as we know it on our planet, including plants, but what is the best water for growing plants? It stands to reason that the quality of the water that you give your cannabis plants directly influences the quality of the final result. People generally tend to use the first water that they can get their hands on, which is usually tap water – combined with the fact that people usually add loads of different products to the water in order to feed their plants without checking pH or EC, this can be disastrous. Your plants will be more likely to catch plant illnesses and attract insect and fungi infestations, which can lead to terribly quality flowers once harvested.

In order to guarantee quality flowers and to make the most out of the nutrients used, the most important thing is to make sure that you know the type of water you’re going to use, and its contents. Secondly, you’ll need to work using specific pH and EC levels so that your plants can absorb everything they need; these levels vary depending on the phase your plants are in and depending on the strain grown. This is why you absolutely need pH and EC meters when growing cannabis, although this post is more about different types of water and how they can be used.

What’s the Best Water for Growing Plants?

We’re going to go through a few different types of water that you can use when growing plants, whether they’re cannabis, flowers, aromatic or decorative plants – many people have misconceptions regarding this issue.

Tap Water

best water for growing plantsTap water is probably one of the most used types of water when it comes to watering cannabis, as it’s definitely the easiest to access. Whether you should use this type of water or not depends on where you live, as the water in certain areas has different characteristics than others. You should be able to check this at the town hall or through town officials Tap water can be hard, (EC + 0.8), medium (EC + 0.4) or soft (EC – 0.4), and it generally has a pH of over 7.0 as well as containing a lot of products that help keep it clear. Tap water also contains lime, chlorine and fluoride in some cases, which can kill natural life in soil and decrease its quality.

In order to water your plants using tap water you can do various things; let the water sit for about 24h so that some of the minerals and other components have time to fall to the end of your tank. The second thing that you can to is you can use an osmosis filter in order to clean your water and make it potable for both people and plants.

Distilled Water

best water for growing cannabisDistilled water is sold in supermarkets and drug stores, and it doesn’t contain any minerals or any other type of microorganism, bad or good. This water is perfect for plants and can be consumed by people although due to the fact that it contains no minerals at all it’s not recommended for continuous consumption. In order to use it on plants, all you have to do is keep in mind that it generally has a pH over 7.0 and an EC of 0.0, so we recommend adjusting the pH and adding calcium and magnesium until it reaches 0.4 EC.

Distilled water is obtained through a process of distillation, which essentially heats the liquid up until it becomes vapor. The vapor is then cooled down in order to retrieve the water, with every other component having evaporated.

Air Conditioner Water

Air conditioner water is taken from your very own air conditioner, and you can use this water when it comes to watering your cannabis plants, as it’s essentially distilled water, although we always recommend using an EC meter; depending on how old the AC unit is or its design, it may actually have an EC of 0.4 rather than 0.0. Its pH is usually over 7.0.

best water for growing plants

Reverse Osmosis Water

Reverse osmosis is a type of water that’s similar to distilled but not quite as pure, as it doesn’t eliminate 100% of all minerals (lime, chlorine etc.) and other impurities in water, but it’s incredibly similar and you can get it from your own type by simply getting a decent osmosis filter and setting it up. Depending on the filter and how long it’s been there for, osmosis filters tend to produce less than 0.4 EC and around 7.0 PH, so you can drink it if you want and you can use it to water your plants without needing to modify it at all.

Reverse Osmosis water is obtained by using filters that trap the minerals and other unwanted elements in the water; depending on the filter and the model, the water will be more or less pure, and therefore higher or lower quality. Reverse osmosis water is always a better bet than tap water or water that you can get from rivers/lakes etc.

Rain Water

rain water for cannabisRain water, as the name suggests, is water obtained straight from nature herself, filling tanks up with rain which you can store and then use at a later date. This water is generally not potable, although some studies would suggest that it is. Regardless, it can be used to water pretty much any type of plant, as when rain is gathering it tends to automatically eliminate any harmful elements, plus plants in nature grow using rain water; rain water is one of the cleanest fresh waters on earth. It tends to have a pH close to 7.0 and an EC no higher than 0.4.

In order to get the highest quality rain water possible you’ll need to set up a water collection system, which will need to stay as clean as possible in order to avoid absorbing elements that could decrease the quality of the water. You can also have it set up on an impurity filter. We recommend using rain water obtained outside of cities, as the rain that falls in the city is usually contaminated as it falls through an already contaminated environment.

Well, reservoir, spring water etc.

well water for cannabisWater obtained from wells, springs, reservoirs and other similar sources is not entirely recommended unless you actually know its composition via a study done in your area; you need to know its mineral and chemical content. This is absolutely necessary, as it may have been contaminated using chemical insecticides or mineral fertilizer, which might render it useless for your plants. Plus, these types of waters tend to contain large amounts of bacteria, fungi, virus and parasites due to animals and possibly even people.

In order to use this type of water we highly recommend studying it beforehand and then, if necessary, treating the water or preparing your storage area to avoid bacteria from spreading. If it’s a well that you own, you can empty and treat the surface using ultraviolet light, or you can also treat it with chlorine. If it’s a spring or reservoir or somewhere public, you’ll need to talk to the authorities in the area in order to figure out its contents and take the necessary measures if the water isn’t apt for plants or life in the area.

River Water

River water may sound like a great idea for watering your plants at first, and maybe even for drinking, although this is not recommended at all. Rivers are generally kilometers long and can have stretches in which they’re contaminated by pesticides, industrial areas or factories that use the water for residues; rivers can also contain dead animals which contaminate water due to decomposition.

On the other hand, the location of the river can give its water unique characteristics; you’ll never find the same type of water in two different rivers. Plus, due to the content of certain minerals, it’s probably more than likely not apt for cannabis growing and you’ll need to analyze all of its contents, not just pH and EC.

In order to use river water you should probably live near somewhere where your town hall can assure you that the rivers don’t contain any sort of contamination caused by human kind. If you nonly have access to water that’s in rivers near or in cities, we highly recommend avoiding using it.

bottled water for cannabisBottled Mineral Water

Bottled water is obviously designed for people to drink, although it’s not the best option for cannabis plants. Still, it’s better than using unknown tap, river, or well water. Mineral water is guaranteed to contain no harmful substances, and its EC levels are lower than 0.5, with a pH around 7-0, although it may have high amounts of different minerals which may end up affecting how your plant grows and how the soil behaves, such as calcium.

In order to work using bottled mineral water you need to choose a brand that has the lowest amount of minerals, and you need to adjust the pH and EC like you would with any other type of water; it’s easy.

The Best Water for Growing Plants

So, after going through various different types of water you can use when growing cannabis, including some you may not have thought of, the best water for growing plants is clearly reverse osmosis or distilled water. These two types of water can guarantee that your plants aren’t getting any toxic minerals or anything they shouldn’t get unless you’re adding it to the water – it also makes it easy to give your plants a 100% controlled diet. Let’s have a look at our ranking of the type of water you should use for growing your cannabis plants:

  • Distilled water
  • Reverse osmosis water
  • AC Unit water
  • Bottled mineral water
  • Rain water
  • River water
  • Well, reservoir etc. water
  • Tap water

This ranking is of course just an estimate, and the different types of water mentioned in this post may vary in position depending on their individual characteristics related to location and environment.

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7 replies on “Best Water for Growing Plants | Cannabis”

Super helpful. I’m a new grower and VERY glad I read this. Thank you . The article did not mention Purified water vs. Distilled water? Still not sure if Purified Water is ideal or not?

The ideal is to start from a soft water with a low EC of 0.2-0.4 mS / cm² and a pH between 6 and 6.5, thus we make sure that the water is not saturated with salts, the proportion of fertilizer being higher or food that we add without creating an excess. And at the same time adjusting the pH we make sure that all that food will be assimilated by the roots.

The distilled water makes it so you can add the nutrients so you don’t have to wonder if they are getting to much or not enough distilled water is cheap and if you plan on keeping up with it you can purchase small distilleries for your home so you can make your own and the nutrients you can find on Amazon and you can find if you have hydroponics stores around or stores similar to them like the organic nurseries

Seedlings. I am on Well water. ppm 250 ish, ec .5
2 week old seedlings, about 2 inches in height.
No nutes. Root Riots to germinate, just put them into a 1.5 pint container with Fox Farm Ocean.
If I switch over to distilled water, the distilled water will have no EC vaule, or very low and or a very low ppm.
Is just the nutes contained in the FF soil going to be enough to feed the wee lil buggers.
I have not had my water tested, but it seems to have a very high content of Calcium ie bad calcium stains in our shower, sinks and humidifier. Humidifiers now get distilled water.
Question is, my seedlings being only 2 weeks old, will distilled water be to low in ppm. I hate to add nutes to the babies. So, just let the FF soil do its thing. The growth seems to have slowed a bit, but I could be wrong, I’ve been wrong once before LOL.

Foxfarm ocean is a very hot soil to be planting newborns in, you should use Foxfarm happy frog instead, it’s a little less hot, kind of warm, when you transplant into your larger 3-5 gallon pots do a 50/50 mix of happy frog/ocean. If you use these soil’s don’t use any other nutrients for the first 5–6 weeks. As far as water are you sure those stains aren’t from heavy iron? Either way you should deathly get a pH tester and make sure you were just the pH in the water to 6. Either way you should deathly get a pH tester and make sure you adjust the pH in the water to 6.4-6.7. You can get pH up and pH down to do that. Also if the PPM in the water is real low, your plants will be unable to absorb any nutrients at all and will starve. You should use bottled water instead of distilled and adjust pH of that. Oh and your plant when 4–5 weeks old will start needing a song Cal-mag added to the water. Happy growing,

i have a bag of FF Ocean as well, and read that its a soil we want to use later on in the vegetative stage of their life cycle. Ive had 3 germinated seeds die on me sown directly in FF Ocean prior to reading up on it. Ended up reading that a low nute soil is best for germination, then moving to FF Ocean after a few weeks or so. I have a few week old plant now and its showing signs of nute burn though, and ive only added minimal additional nutrients to it since i was concerned about pre-existing conditions of low nitrogen levels. Turned out it was nute burn to begin with, since i started the plant on FF Ocean way too soon.

i use tap water that sits for 24 hours and then when i switch to flower i go with distilled and then i know what exactly what is going into plants, and during wash i go with plain distilled water with no nutes close to when i know when i am going to harvest.

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