By Max Sargent


Everyone knows that plants love water. And cannabis plants are no exception! One of the first things you need to figure out when setting up a grow is where you will source your water from. To decide this, you’ll need to know what it contains in terms of impurities and minerals, and what its pH level is.

Choosing a water source is about figuring out what kind of grow you want. Some can handle lower-quality water, while others necessitate something much purer.

In this article, we list several sources of water, explain their pros and cons for growing weed plants, and assess which types of grow operations they might be suitable for.

Cannabis And Water Quality Part 3: Choosing A Water Source
Cannabis And Water Quality Part 3: Choosing A Water Source

How to Find the Perfect Water Source for Your Grow

First, when choosing a water source, you need to know what you have access to. It would be wonderful to have the perfect spring in our gardens, but most of us don’t. Most of us don’t even have gardens.

Second, you need to know what you can comfortably afford. A reverse osmosis filter would be great, but do you have £5,000 to spare? Always choose the cheapest, suitable water source!

Third, you need to know what your setup will require. A casual soil grow is robust and can handle many types of water, so long as you water properly. A hydroponic grow, on the other hand, is much more susceptible to contaminants and fluctuations in fertiliser and pH levels. As such, much purer water is required.

Knowing where you stand with the above considerations will help you to choose the appropriate water source for your grow.

Cannabis And Water Quality Part 3: Choosing A Water Source

Different Water Sources for Growing Cannabis

Most of us are used to sourcing all of our water straight from the tap, to the degree that we hardly even notice it. While this luxurious supply of clean water serves most of our needs perfectly, it may not always be the best choice for those who want to grow cannabis.

There are many different ways to source water for weed plants, each providing certain benefits and drawbacks.

Rainwater

Is rainwater good for cannabis plants? In many cases—yes! It’s very possible to collect rainwater using a water butt. This can either be placed on a roof or somewhere in the garden. Collecting rainwater is fairly effortless and totally free, and on top of that, the quality of the water tends to be pretty high.

If you can collect rainwater, it’s about as good as it gets. Think about it; where do plants get their water from in nature? Rain!

As rain forms, it tends to shed any impurities, meaning it is a clean and reliable source of water.

Cannabis And Water Quality Part 3: Choosing A Water Source

Pros of Rainwater for Growing Weed

  • Very clean
  • Stable pH of around 7.0
  • Free
  • Plentiful in some regions
  • Easy to collect—if you have the space

Cons of Rainwater for Growing Weed

  • Collecting rainwater can be illegal in some places
  • Supply may not be plentiful in some regions
  • pH may need adjusting for hydroponic grows
  • Impossible to collect if you don’t have the space

How to Prepare Rainwater for Growing Weed

Rainwater is pretty much ready to be used. The only situation where you’ll likely have to adjust it is if you’re growing hydroponic weed. In this case, the optimal pH level is 6.0, which is lower than rain might naturally be.

But besides a slight pH adjustment in this instance, rainwater needs no preparation.

Best Suited For

Rainwater is best suited for those growing organically in soil. It doesn’t require adjustment and won’t harm important soil microorganisms. It’s also very good for those growing on a budget, so long as you have somewhere to place a water butt.

Tap Water

In most cases, tap water is the easiest water source for growing weed. All it requires is for you to turn on the tap. What’s more, for those who aren’t on a water meter, the extra water required to grow cannabis costs no more than a normal amount of water. In this sense, it can basically be free.

The main issues with tap water for cannabis are that it often has a high pH, and it may contain compounds that can be damaging for a grow, such as chlorine.

Cannabis And Water Quality Part 3: Choosing A Water Source

Pros of Tap Water for Growing Weed

  • Either very cheap or free
  • Incredibly easy and accessible water source
  • Often fairly clean

Cons of Tap Water for Growing Weed

  • Usually has a high pH
  • May contain compounds such as chlorine
  • Might contain minerals that throw off feeding

How to Prepare Tap Water for Growing Weed

If you use tap water, you should first test the pH. If you find that it’s above 7.0 (which it often is), you must use a "pH down" solution to reduce it to around 6.5. If you’re growing organically, then a high pH is less of a problem, as bacteria in the soil help the plant to absorb nutrients.

However, tap water often contains chlorine, which kills off beneficial bacteria in the soil. So if you’re growing organically, find out if your tap water is chlorinated. If it is, it can still be used; simply leave your tap water to sit in an open container for 24 hours. During this time, all of the chlorine will evaporate, and it will be suitable to use.

Some tap water, especially in cities or limestone regions, contains an abundance of minerals. In some cases, especially hydroponic grows, this can throw off feeding ratios and potentially cause overfeeding. In soil grows, this is less likely to be a problem. An EC meter can tell you the mineral content of your water, which will help you to determine whether it is suitable to use. If your water source is rich in minerals, there’s not much you can do to remove them. You’ll just have to adjust feeding.

Best Suited For

Tap water is a great all-rounder. For most growers, especially soil growers, tap water is probably the cheapest and simplest choice. And for beginners, it is totally recommended.

Distilled Water

Distilled water is 100% pure. It contains no minerals, compounds, or bacteria; it has an EC reading of 0.0. For this reason, it can be the perfect tabula rasa when it comes to growing cannabis. You can add the minerals and nutrients you want, and adjust the pH easily.

However, it’s expensive, and overkill for many growers. Plus, having an EC reading of 0.0 isn’t always a good thing. The minerals in most water sources can be useful for growing, and starting out with nothing can be a hindrance for those who don’t want to go the extra effort of adding tiny amounts of minerals to their water source.

Cannabis And Water Quality Part 3: Choosing A Water Source

Pros of Distilled Water for Growing Weed

  • A perfect blank slate for those who want to fine-tune their grow
  • Great for hydroponic grows
  • You know exactly what you’re working with

Cons of Distilled Water for Growing Weed

  • Expensive
  • Unnecessary for most grows
  • A total lack of minerals is not always helpful
  • pH often needs to be adjusted

How to Prepare Distilled Water for Growing Weed

Distilled water may have a pH of above 7.0, so you’ll still need to check and, potentially, adjust it. Furthermore, many growers add calcium and magnesium to distilled water in order to bring it up to EC 0.4.

Besides these two points, distilled water needs little in the way of preparation.

Best Suited For

Distilled water is only really recommended for expert growers who want to start from 0 and add everything themselves—usually in the context of a hydroponic grow. Unless you know what you’re doing, using a water source this pure can be counterproductive, and it’s definitely a waste of money.

Reverse Osmosis Water

Reverse osmosis (RO) water is created by using pressure to force water through a semipermeable membrane. The water gets through, but most of the impurities stay behind. As such, RO water is very pure—though not as pure as distilled water.

You can buy RO water, but you can also have a filter fitted in your home so that it runs out of your taps. These filters tend to last for several years, and as such are fairly expensive.

Cannabis And Water Quality Part 3: Choosing A Water Source

Pros of Reverse Osmosis Water for Growing Weed

  • Very pure
  • Very accessible once you have a filter fitted
  • Great for hydroponic growing
  • pH of around 7.0

Cons of Reverse Osmosis Water for Growing Weed

  • Initial cost of having filters fitted is expensive
  • Overkill for most hobbyist growers

How to Prepare Reverse Osmosis Water for Growing Weed

RO water has a pH of around 7.0, which can work very well for soil grows. However, for hydroponic grows, this will need to be adjusted with a pH down solution. And, depending on the type of filter, this water may have an EC count of lower than 0.4. In this case, as with distilled water, it is recommended to add calcium and magnesium to bring it up to this level.

Best Suited For

RO water is great for hydroponic growing, as it can be sourced directly from the tap. This makes it much more efficient than distilled water (which comes in bottles). This becomes even more useful for those growing on a large scale, where a lot of water is needed.

Bottled Mineral Water

Some growers give their cannabis plants bottled mineral water. While this tends to be a very luxurious option, it does have the benefit of being rich in good minerals and low in potentially damaging compounds, such as chlorine. That being said, the best bottled water for weed plants is that with a low mineral content, otherwise you might find you have an overabundance of certain compounds.

Generally though, bottled mineral water is not a good option.

Cannabis And Water Quality Part 3: Choosing A Water Source

Pros of Bottled Mineral Water for Growing Weed

  • Clean
  • Often has a good level of minerals
  • pH of around 7.0

Cons of Bottled Mineral Water for Growing Weed

  • Expensive
  • Wasteful in terms of plastic/glass
  • Usually unnecessary

How to Prepare Bottled Mineral Water for Growing Weed

This will depend on the brand you use. You’ll have to measure the pH and EC levels, and adjust accordingly.

Best Suited For

Bottled water is for those without any other choice. If you have access to another suitable water source, this is almost definitely going to be better than going through hundreds of bottles of mineral water. But if it’s your only choice, the water itself is very good.

Water From a Well or Spring

If you have land that contains a well or a spring, then you have a plentiful and free water source at your doorstep!

For those with access to these water sources, they are a very good option. However, the quality of water from these sources varies massively, and whether it’s suitable will depend on where you are.

Cannabis And Water Quality Part 3: Choosing A Water Source

Pros of Water From a Well or Spring for Growing Weed

  • Free
  • Accessible
  • Plentiful
  • These sources of water tend to be clean

Cons of Water From a Well or Spring for Growing Weed

  • Not an option if you don’t have a well or a spring
  • Varied water quality may make some sources unsuitable
  • As these sources come from the ground, they tend to have a high mineral content
  • Generally not desirable for hydroponic growing

How to Prepare Water From a Well or Spring for Growing Weed

This depends entirely on your water source. Groundwater often has a high mineral content, and this can vary greatly from region to region, as can pH. Therefore, you’ll need to investigate the specifics of your water.

Best Suited For

If you have access to one of these water sources, and it’s suitable, then it is a great choice that gives you a free and abundant source of water. This can be especially helpful if you plan to grow many plants. For those growing hydroponically, groundwater may not be suitable.

River Water

If a river runs through your land, then you may be able to source your water from here. Be aware, though; rivers often aren’t as clean as they look, and tend to be full of toxins and fertiliser from farm runoff.

Smaller streams tend to be much more suitable compared to rivers. Also, the higher up you are, the cleaner the water is likely to be.

Cannabis And Water Quality Part 3: Choosing A Water Source

Pros of River Water for Growing Weed

  • Free and plentiful

Cons of River Water for Growing Weed

  • Few have access to it
  • River water is often contaminated
  • Fertiliser runoff in rivers can make feeding plants very difficult

How to Prepare River Water for Growing Weed

If your river water is clean and suitable to use, then you’ll probably need to adjust the pH and check the mineral content. Once you know the mineral content, you can adjust feeding accordingly.

Best Suited For

Those with no other choice, or those who know they have a clean supply, can look into using river water for their grow. Only people with a clean river that runs high up should use river water for growing weed.

Air Conditioner Water

This may not sound like a clean source of water, but it is! Air conditioner water is essentially distilled water, and as such is very clean and has a low EC reading.

Cannabis And Water Quality Part 3: Choosing A Water Source

Pros of Air Conditioner Water for Growing Weed

  • Free and accessible
  • Very clean

Cons of Air Conditioner Water for Growing Weed

  • You need an air conditioner
  • May not provide enough water for many plants
  • pH is often over 7.0

How to Prepare Air Conditioner Water for Growing Weed

The pH level of air conditioner water is usually over 7.0, and will therefore need to be adjusted with a pH down solution. It’s also worth checking the EC reading and adjusting it as necessary.

Best Suited For

Those who have a small number of plants can opt to use water from the air conditioner. Though this option works, it’s not always the most reliable nor the simplest solution.

Signs of Water Problems in Your Cannabis Grow

Many novice growers tend to overwater their plants, thinking that more water is better. Far from it!

Watering too regularly restricts the amount of oxygen in the soil, eventually causing the plant’s roots to rot, which is often fatal. Wait until the top 2cm of soil is dry before watering your plants.

If overwatered, leaves will begin to discolour and sag, moving from the bottom of the plant upward. They will appear brown and wet, rather than yellow and dry.

Furthermore, if your water source is off in terms of pH, EC, or PPM, over time, this can restrict your plant’s ability to uptake food properly. The signs of this are manifold. If you notice discolouration of the leaves or poor growth, then you may well have a nutrient issue. Your water source might be the cause.

Bottom Line: What Is the Best Water Source for Growing Cannabis

It depends on what you have access to, and what you’re trying to achieve.

For most growers, we’d say that tap water, with the necessary adjustments, is probably going to suffice. An alternative water source is usually only necessary if you have very specific requirements, your tap water is of low quality, or you have access to another, better water source.

For those who need a very pure supply of water, rainwater, RO water, and distilled water are probably the best options.

If you’re new to cannabis growing, don’t get carried away trying to perfect everything at once. Stick with tap water, and spend your time and money honing other skills!

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