How to Get the Best Water for Marijuana Plants

January 27, 2021

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. 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.

Signs of water problems in plants

water problems in weed plants
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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.

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Types of water for weed plants: Soft and hard water

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

What does hard water do to cannabis
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 is in a liter of the water. So, 200-400 mg/L is the range for hard water while 400-550 mg/L is for very hard.

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.

Soft water

soft water on cannabis
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.

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

Reverse osmosis and ionic settings for weed
Reverse Osmosis and Ionic Filters – Image powered by

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. 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 weed plants
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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.

Download my free Grow Bible for more more troubleshooting tips

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

High Sodium Concentration for weed plants
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As mentioned, high sodium can be damaging to the cannabis crop. But an extremely dry soil with salts can be fatal. 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

High Sulfur in the Water
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Water that smells like sulfur is highly acidic and can easily weaken the plants. To be sure, use a pH meter to confirm the suspicion, then add lime to the soil make it less acidic.

Chlorinated water

Chlorinated Water
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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.

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 a pH and TDS testers.

Grow healthy weed plants from seed to bud! Start from choosing high-quality seeds from my seed bank.

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.

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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.

The founder of I Love Growing Marijuana, Robert Bergman, is a marijuana growing expert that enjoys sharing his knowledge with the world. He combines years of experience, ranging from small-scale grows to massive operations, with a passion for growing. His articles include tutorials on growing... [read more]


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  1. By James ,12 Jul 2014
    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 […]Read More
    1. By Anthony ,11 Dec 2019
      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.
  2. By Jeremiah ,29 Mar 2015
    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 […]Read More
    1. By Jawbone ,02 Jul 2021
      What is the verdict on the lake water. I'm considering doing the same.
  3. By The? ,20 Jul 2015
    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 […]Read More
  4. By latewood ,23 Jul 2015
    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 […]Read More
  5. By Symptom Checker – Identify Marijuana Plant Problems ,24 Jul 2015
    […] Hard or soft water […]
  6. By When And How To Water Marijuana In Soil ,03 Aug 2015
    […] 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 […]Read More
  7. By kcaven ,10 Sep 2015
    Can bottled water be used? Distilled? Regular? thanks!
  8. By latewood ,12 Sep 2015
    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; […]Read More
  9. By chris ,03 Oct 2015
    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 […]Read More
    1. By Steve Dutch ,11 Mar 2016
      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 […]Read More
      1. By Jennifer ILGM ,14 Mar 2016
        Hi Steve, Im not sure what you mean, but can you email pictures with more detailed information to support at [email protected], so we can take a look at it.
    2. By ken ,16 Nov 2017
      plants will grow strange after forcing veg state you may even see round leaves. perfectly normal.
  10. By latewood ,05 Oct 2015
    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 […]Read More
  11. By kman ,10 Oct 2015
    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 […]Read More
  12. By Problems That Cause Marijuana Plants To Stress ,18 Nov 2015
    […] 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 […]Read More
  13. By Lucky ,31 Dec 2015
    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 […]Read More
  14. By Ak47luver ,12 Jun 2016
    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 […]Read More
  15. By latewood.ILGM ,08 Aug 2016
    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 […]Read More
  16. By latewood.ILGM ,08 Aug 2016
    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 […]Read More
  17. By sen ,26 Oct 2016
    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
  18. By 1BigFella ,07 Sep 2017
    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 […]Read More
  19. By Adamant ,08 Sep 2017
    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 […]Read More
    1. By latewood_ILGM ,26 Sep 2017
      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 […]Read More
  20. By Camille A.W. O’Hara ,21 Sep 2017
    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 […]Read More
    1. By latewood_ILGM ,26 Sep 2017
      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 […]Read More
  21. By VASILEIOS vasileiadis ,06 Oct 2017
    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
  22. By James G ,28 Mar 2018
    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 […]Read More
    1. By latewood_ILGM ,18 Apr 2018
      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 […]Read More
  23. By Tricia Fisk ,30 Aug 2018
    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 […]Read More
  24. By M Ernandes ,09 Mar 2019
    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!!
  25. By Tilton ,25 Mar 2019
    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 […]Read More
  26. By Elliot ,29 Mar 2019
    How much extra calmag would you add Aditionaly if your ppm is 150
    1. By latewood ILGM ,03 Apr 2019
      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 […]Read More
  27. By Joshua ,08 May 2019
    I use a Britta water pitcher for my plants and use tap water. I only have 3 plants but it seems to work well.
  28. By Evo Heal CBD Oil ,09 Aug 2019
    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 […]Read More
  29. By Bill ,03 Oct 2019
    Does anyone know theexact placemen in a 400w hps
    1. By Latewood_ILGM ,17 Oct 2019
      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 […]Read More
  30. By Gene Matfield ,22 Apr 2020
    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
  31. By Tvrt ,24 Jul 2020
    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!
    1. By Larry ,28 Jul 2020
      Can you use water from a dehumidifier or from air conditioner?
      1. By Randy Koochamondo ,16 Sep 2020
        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;)
  32. By Kyle ,01 Jan 2021
    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!

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