Best water for marijuana plants

Reading time: 9 minutes

Along with light and nutrients, water is vital in the nourishment of marijuana plants.

Aside from assisting in photosynthesis, it also keeps the plant’s internal temperature cool.

Most importantly, it carries all the nutrients in the soil to the roots so that it can consume what it needs.

So, read more below to find out what the best water for marijuana plants is.

Therefore, the type of water we use significantly affects the nutrition of the plants.

As such, we must ensure to hydrate the crop using only the most suitable kind.

This is especially valuable when we want to produce huge buds that are rich in THC.

In general, many types of water are available for the growers to use.

Watering marijuana plant
Watering cannabis

This includes tap water, rainwater, purified, and distilled.

When it comes to availability, all of them are accessible and cheap.

But which one gives the most desirable outcome in growing marijuana?

In this article, we will explore the different kinds of water and how they affect the plants.

Also, we will learn how to balance and correct common water problems to make them optimal for the crop.

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Choosing the best water for marijuana plants

As mentioned, the quality of water is crucial for the healthy growth of plants.

Hence, this section will discuss its various types and their specific traits.

This way, we will be aware of their properties and make informed decisions on which type to use.

But first, we must know the signs that the plants are suffering from poor-quality water.

Signs of water problems in cannabis plants
Signs of water problems in plants

Signs of water problems in plants

Overall, the plants will look weak and wilted.

Also, they may exhibit signs of various nutrient deficiencies.

In worst cases, they will stop growing and we can say goodbye to our dream of harvesting some buds.

Types of water for weed plants: Soft and hard water

Basically, there are two main types: soft and hard water. Interestingly, their names have nothing to do with how they look or feel.

Types of water for weed plants
Types of water for cannabis plants

Rather, we base the classification on the concentration of minerals that they contain. The unit of measurement for this is 1 mg/l of contaminant = 1 ppm.

Many beginner growers struggle to know when the best time to water their marijuana plants. We’ve put together this Cannabis Watering guide to help!

Hard water

We define water that has a high content of dissolved minerals as hard.

Primarily, hard water contains high calcium and magnesium content.

To measure its hardness, we look at how many milligrams of calcium salts there are in a liter of water.

So, 200-400 mg/L is the range for hard water while 400-550 mg/L is for very hard.

Hard water for growing cannabis
Hard water for growing marijuana

In general, tap water floats along the range of 170-390 mg/L.

While it is not dangerous to humans, consuming this type of water can be harmful to cannabis.

Oftentimes, calcium deposits in the roots may block the absorption of other nutrients. If not corrected, this usually results in nutrient deficiencies.

Thus, we must soften hard water to render it more suitable for the crop.

If your plant problems cannot be resolved by adjusting the amount of sunlight and water, try our complete fertilizer set to correct nutrient deficiency.

Download my free Grow Bible for more troubleshooting watering tips.

Soft water

Opposite to hard water, soft water contains very little minerals to none at all.

According to the water hardness scale, less than 150 mg/L is very soft, while 150-200 mg/L is simply soft.

A good example of soft water is rain, but it eventually becomes filled with various minerals as soon as it hits the ground and runs in the soil.

In any case, it is one of the best types of water for plants. Other great examples are purified, ionized, and distilled water.

watering cannabis plants
Watering marijuana plants

How to balance water for your weed plants

Finding the correct balance of hardness in water is a challenge for many growers. For cannabis plants, the perfect water is soft, within the range of 100-150 ppm or mg/L.

Unfortunately, tap water in the mountains, by the sea, or in big cities usually goes beyond this range.

So, how do we make hard water soft? The following methods will show us how.

Reverse osmosis and ionic filters

While we can soften water using softeners, this is potentially harmful to the plants.

In this process, sodium is an essential ingredient that removes calcium and magnesium.

However, sodium salts can build up in the soil and attach to the roots over time.

Worse, the high salt content fools the plant into thinking that it has ingested enough water.

Reverse osmosis for watering marijuana plants
Reverse osmosis

In effect, the plant will die from thirst. Thus, using special water systems such as reverse osmosis or ionic filters is preferable.

Other reliable systems are carbon filtration and distillation.

Essentially, they purify hard water by safely removing all the minerals, salts, and other impurities.

Hence, we get pure water that allows the plants to completely absorb nutrients in the soil.

Also, it preserves the health of the roots.


cal mag for watering marijuana plants
Cal-Mag – Image powered by

Oftentimes, the methods mentioned above make the water too soft.

Since 100-150 ppm is the ideal range that produces healthy cannabis, we must adjust the hardness level by adding Cal-Mag.

So, using a TDS meter, test the number of dissolved solids in the water and adjust it to the right value.

Know how to perfectly time your harvest so you can maximize your yield. Download our free mini harvesting guide

Correcting water problems for weed plants

Unfortunately, growers must deal with several problems regarding water quality.

Often, the issue stems from a high concentration of certain minerals present in tap water.

Luckily, there are easy ways to fix them.

High sodium concentration

As mentioned, high sodium can be damaging to the cannabis crop.

But an extremely dry soil with salts can be fatal.

Testing sodium in the water for marijuana plants
Testing water for sodium

To alleviate this problem, feed the plants filtered water to help dilute the high mineral concentration.

For a more lasting solution, improve the soil drainage and switch to using well-balanced water.

High sulfur in the water

Water that smells like sulfur is highly acidic and can easily weaken the plants.

water quality for growing marijuana
Testing water for sulfur

To be sure, use a pH meter to confirm the suspicion, then add lime to the soil to make it less acidic.

Chlorinated water

In most cases, tap water contains certain amounts of chlorine.

But when the concentration is too high, this can kill a lot of beneficial bacteria that assist the roots in absorption.

In addition, when the sun is too hot, the chlorine may react by causing nutrient burn.

testing water for chlorine cannabis plant
Testing water for chlorine

To fix this problem, use activated carbon filters or chemicals that remove chlorine.

For some growers, letting the water sit overnight usually does the trick.

But the best solution would be to invest in a reverse osmosis system to get the best type of water all the time.

The right water produces happy weed plants

To sum up, good-quality water is vital to get healthy plants that produce high yields of potent buds.

Fortunately, even if we only have access to tap water, there are ways to adjust it to become more suitable for the crop.

For best results, invest in special water systems and mineral measuring equipment such as pH and TDS testers.

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Now that we know how to achieve the best type of water for marijuana plants we can be confident in feeding it.

If we start with good seeds and provide the basic needs, using well-balanced water will further help them thrive.

So, practice this skill consistently and enjoy a successful harvest by the end of the growing season.

FAQ about the best water for weed

Is distilled water good for weed plants?

Yes. Distilled water is an example of soft water, which is great for weed plants.

What’s the best water filter for growing weed?

Reverse osmosis or ionic filters are some of the best water filters for growing weed. However, you can also use carbon filtration and distillation to purify hard water.

What is the best water for growing plants?

Soft water is the best water for growing your weed plants. Some examples of soft water are rain, distilled, purified, and ionized water.

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Robert Bergman

Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations. His passion for growing led him to develop his own Gold Leaf strain. Now, Robert is dedicated to sharing his knowledge with the world.... [Read full bio]

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49 comments on “Best water for marijuana plants”

  1. I live in a place called Pittsfield it’s in Berkshire county in Western Massachusetts my tap water right now comes out of the faucet at 68 to 66° f in around 78 parts per million year-round!

  2. If you believe in yourself then with the help of ” i m a g i n a t i o n ” a tear drop in any H20 formula is guaranteed place a smile on your plants face;)

  3. I started to use reverse osmosis water for my outdoor plants, and i did bingo, i never had plants like these…tasty big buds and beaytiful plants!

  4. got weeding cake seeds growing for 5 wks. now barely grow 2in. leafs are bright green to not quit yellow I need help I used Pre mixed organic potting soil and use a T5 light is it a watering problem

  5. Yes can u please tell me what the name of this filter is ur talkin about or what is the website that u are referring too.

  6. Bill, This is a topic for water. Not sure what you are asking. Please proof read your comment before posting it in the appropriate topic of the blog. Meanwhile; I will guess you meant exact placement of a 400w hps…This can vary. Do you have an air-cooled hood? do you have glass in front of the lamp? Most of the time we set 400w HID lamps 24-32″ above the canopy. place your hand palm down at the top of your canopy. If the backside of your hand is cool…lower lamp a couple inches and test again. Adjust accordingly. If your hand is hot…Raise lamp a couple inches and test again. Hope this helps. Join our support forum for educated and enlightened support ofr successful growing. 🙂

  7. Hey there! I could have sworn I’ve been to this
    website before but after checking through some of the post I realized it’s new to me.
    Anyhow, I’m definitely delighted I found it and
    I’ll be bookmarking and checking back often!

  8. I use a Britta water pitcher for my plants and use tap water. I only have 3 plants but it seems to work well.

  9. Elliot, Why do you want to add CalMag to a ppm of 150? Just increase your nutrient level and the nutrient you use will have and thus add more CalMag. CalMag is often overused when it is not necessary. I suggest you join our support forum, where we can help you grow successfully. Happy growing

  10. I just have tap water i don’t have to have all that exspensive Equipment. You people try and make it sound so hard and Exspensive to grow good herb. New grower you dont have to have all that To Grow good outdoor herb.

  11. Thank you Mr Bergman, You taught me so much in such a short time. Reading is great knowledge! Especially reading something as wonderful as this plant! I just started growing. And with tips from you my plants are booking!!

  12. I have a reverse osmosis system but it seems like i get them perfect then use the ros water they start having problems i have hard water so i got the ros because everyone said hard water is not good for plants if thats the case why do they do better with my tap water than the ros water? Confused

  13. James,

    I don’t know what to tell you. If you ppm went down to almost nothing after you added nutrients; I would say your meter is fried. I honestly do not know Go here: and we can help you in a more broad way. There are many details you left out and so I cannot give you an informed answer here.

    See you in the support forum 🙂

  14. I use dehumidifier water, pH is 6.3 constant and hardness is .53 ppm appr. My concern is, I added soluble food to water the plants, the pH didn’t change but the hardness went to .13ppm I can’t figure out what ppm means they have the right concentration of nutrients now. I was told the starting ppm for seedling is 250ppm and mature is 700-1200ppm, What am I supposed to do? Somebody help!!

  15. i already downloaded your bible which is perfect as far as i read.Thanks a lot dear sir for so gentle gesture.Live long stay strong and high

  16. Camille A.W. O’Hara,

    Salt on the rockwool is just because the top is dry and you see residual salt. I suggest you join our forum and post your questions. There are some small qualifications you must meet before posting a new topic but, it is not too bad.

    We can help you there. In order to help you we need more info than can be shared in this blog comment section. I hope you join up. Happy growing. 🙂

  17. Adamant,

    You sure do not want to add that much phosphate. Looks like you need to amend the Nitrogen most of all. However you are missing several other essential minerals. Seems like pretty good soil to start out with. I suggest you contact your county agent and ask him what he would add to the coil you wantr to grow veggies in.

    Happy growing, 🙂

    p.s. Join our forum. we can help there also.

  18. I am using rock wool and rocks as my growth medium. I started out with purified water but the salt cause my last batch to be stunted and they never produced buds. So I started over, not realizing then that the purified water was the problem. I read here to go to distilled water so I did. I have salt on my rock wool and the bottom of the stem. Help, how do I get it off? I tried flushing it but I don’t want to screw up and ruin the rock wool. I really need advise! Thank you in advance!

  19. Ok so soil sample from 4/10/
    ph 8.2
    Nitrate nitrogen med/high12ppm
    ammonium nitrogen low 12ppm phosphorus high100ppm
    Potassium very high 250ppm
    Calcium high 1600
    Magnesium high125ppm
    Any suggestions? Things are nice but if theres more i could do for the girls.. and the rest of veggies.. then why not. I do have a little 9_50_10 essential oils stuff that a friend gave me.

  20. One thing about Colorado River water is you never need to add Epsom Salts: It has lots of Calcium and Magnesium already. Another important thing to know is that most home water softeners get rid of calcium and magnesium by replacing them with sodium! NEVER use that water for plants.

  21. hi,can u please help me with a report here,,um struggling to find related reports for my literature topic is effects of hard water(not saline) on growth and yield of tomatoes

  22. Cheis,

    Rain water is great, however, you still need to test the PH and make sure you are collecting this rain water in a potable water reservoir, ro at least food grade. 55 gallon soap drums are acceptable vessels for collecting rainwater.

    Check that PH. If you need more information. Join our forum 🙂

  23. Ak47luver,

    Sorry to have missed this. We have been having a chronological issue with our blog for a couple months.

    You always want to feed bloom nutes in flower. Hope everything turned out alright.

    For more available knowledge; Join our free support forum. So much great advice there! 🙂

    Happy growing

  24. Hey Mabey you can help I had female super skunk indoors under 24,hours cfls I put it outside on May 1st it started flowering within 2weeks and is still in flowering on June 10 it’s like 15 + hours a day of light I live in USA down south is it possible that the plant will stay in flower to maturity if it does go back into veg what do I do with the flowers also do I feed it bloom food are veg food now why it’s in flower

  25. Hi Sir ,

    When plants have less fingers on there leafes it are 2 things or mayby 3.
    1/ not enough light or not the right collor light
    2/ the strain growht as 1 finger leafes ,i thought some Dutch company has that strain.
    Something with ‘duck’ in the name. If you see the plant you woudnt say its a cannabis plant. But it is …do you know what strain there is being given to you?
    3/ other opinion
    Regards Steve

  26. Soft water with chemicals(which are acidic)lead to acid enviroment bcs soft water doesnt have enough alcali salts to compensate acid from fertiliser…If u have distiled water(without any salts) and mixed with ferts,you had to much acid enviroment(distiled water get same ph from water&ferts which you mixed)…to not have that,you must have correct ec-meter to measure your ec/ppm…150 ppm=0.3ec on meter.That alkali salts in water(mg,ca…)compensate acid from ferts and they are dancing in good way if you have acceptable ph(5.6-6.5)…If you wanna good results you must have ec and ph meter and measured once a week water,soil,water&nutrients when you irrigate and your drain tell you the health of your plant,everything develops of tap water for irigate……Robert know how to grow and if u are really want a good result i advising you to read the robert book bcs that man know knowledge!Salut from Cro…

  27. […] If you find out that your water contains undesirable minerals or elements, your best bet is to use filters to purify it. Try to avoid water softeners, as these may fix one problem, but might add other elements you don’t want. Read more on what water to give your marijuana plants. […]

  28. i have moved from hard water area in england to soft area in scotland im in soil and perlite and others in coca am i going to have problems or will soil buffer my nutes or do i go organic or buy new soft water nutes tuvm awaits ure reply in anticipation

  29. chris,

    Really do not have an answer for you.
    you re-vegged a small plant in flower. I would probably cone it.

    I suggest you join our Support forum and post a picture in order for us to see what you are talking about. Then we could make informed recommendations

  30. I have a female clone that wa given to me it was just a few inches tall but had already started to flower so i took it home and put it under 24 hours 400 watts hps and it turned around back into full veg which is what it was supposed to do but the one thing i dont understand is every frawn has only 1 leaf it actually looks mor like a vegetable than a normal plant its growing great but should i just let it go or what? I really hope somebody has a good answer.

  31. Distilled water is perfect for growing. The downside is that you have to constantly buy and tote water every week. This can become tedious.

    Invest in an 4-5 stage Reverse-Osmosis unit. This will provide you with years of pure water; And, at a fraction of the cost and effort of buying, and toting distilled, or bottle dwater

  32. […] When it comes out of the tap, your water could have an EC that ranges from 0.2 to 0.8, or even higher. The real issue here is that even when you take an accurate measurement, there is no way for you to know what sort of elements are in your water, and the ratio at which they occur. This means that all the extra money you’ve spent on expensive, carefully measured nutrients is for naught: the mix is instantly unbalanced by an unknown quantity of other nutrients. In a worst case scenario, this can cause nutrient burns or lock-outs and inhibit the growth of your plants. More info about your water in the articel “Hard or soft water for marijuana plants” […]

  33. Hello The?,

    I would not apply hydrochloric acid to my plant solution. I would stick with phosphoric acid, or go buy a battery refill kit at the auto store. It is pure diluted sulfuric acid , I use this all the time, and even in my greenhouse,

    As far as salvaging a plant with Botrytis ; I suggest that you join our support forum, and copy/paste a “Support ticket” into your post. We have expert growers, and great members that are always willing to help you out. 🙂

  34. where i live in the uk the tap water is f$%#in’ shite. hard as diamond, mmmm, well u get my drift….? i reckon.
    it also has well over 300 ppm of other solids, salts, minerals. gazillions of it….not great.
    gonna get an ro system soon and give that a try, i’ve heard great things about it but i just cant afford one atm. but one day soon as possible.
    i try to save and use as much rainwater as possible for now and soften with nitric/phosphoric acid when i run out. is hydrchloric acid any good for softening, just a thought as i wouldnt be adding the phos and nitric bits out. yeah if anyone can help me with that would be real cool?
    also does anyone know what i can use, safely to save what i can of a plant in bud with a botrytis problem, i’m trying to salvage something!
    have a nice day everyone :- )

  35. I’m using lake water in SW Colorado for our indoor and outdoor plants. The ppm is around 1100 before I add my organic nutrients. It goes up to over 2000 after I add them. Is it necessary to get a filter for that or is it ok, being that it’s minerals from the lake?

  36. Hello Robert – I wanted to alert you to a new filter I have designed specifically for growing cannabis. It will remove chloramines entirely and it will remove or reduce fluoride, depending in part on local water chemistry. In most locations with low tds (under 300) fluoride will be removed. Please check out my website.