Cannabis & Water Quality

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Water quality is an often overlooked aspect of cannabis growing. It can be responsible for so many problems, including those dealing with nutrients. We know how tempting it is to reach for the nutrient troubleshooting sheets and feed your plants more. Put those bottles down, stop scratching your head, don’t panic and ask yourself this back to basics question. “Have I checked my water quality lately?”

In part one of our guide on water quality, we look at why water is important, and how pH affects a grow.


All life on earth is dependent on it. We are all made mostly of water. Even the surface of the earth is more water than land. Cannabis is ninety percent water and uses it in a number of ways to live and grow.

Water transports nutrients, gives the plant its stiffness and lushness or “turgor,” and plays a major part in photosynthesis. During the day, water travels up the stem to the leaves where it evaporates through tiny holes called stomata and is then exchanged for carbon dioxide. This is called transpiration. The exchanged carbon dioxide is then used to in combination with light to create sugars which are the plant’s food; this is called photosynthesis.

How to use Nutrients When Growing Cannabis


This little lesson in biology is all well and good, but what does it have to do with poor water quality? Poor water quality means these processes can’t function properly and the result is a lot less bud for you. So indoor or outdoor, water quality is very, very important.

Many problems stemming from water inconsistencies can mimic other issues that can affect the cannabis plant. Aside from over or under-watering, this can include symptoms of over or under fertilisation, or even heat stress, and it is usually only the experienced grower that can tell the differences at a glance.

So before you go playing with the intricate witches brew that makes up most nutrients, do one simple thing. Check your water.

How to Measure PH of Water When Growing Cannabis


The first factor to look at is pH. pH affects a cannabis plant’s ability to transport nutrients and carbohydrates. The symptoms of either too high pH or too low pH are very similar and can be confused with a number of nutrient problems – the solution to which can have you chasing your tail for weeks searching for an answer. It could just be a wonky pH affecting your ladies’ ability to transport nutrients. We have seen plants with several different symptoms simultaneously and the troublemaker turned out to be bad water pH.

Cannabis thrives at a pH that hovers around 6.5. A little higher or a little lower is okay; in fact, some indicas enjoy a low 6.2, but you can’t go wrong keeping it at 6.5. Modern growing techniques will have you flushing your plants often enough to avoid much pH fluctuation in your growing medium due to nutrient build up, so pay good attention to your water and you can’t go wrong.

Checking your pH is as easy as swishing a pH metre around in your water runoff sample.

There are as many pH testing products as there are serrations on a sativa leaf. Let your budget decide whether you buy a simple analogue probe or a more expensive digital one – with all the bells and whistles.

These metres don’t require any calibration and are ready to go straight out of the box. Just remember to test your runoff water, as this is the correct reading of what your plants are getting at the root system, and adjust at the top end to suit.

If you are doing DWC (hydroponics), regularly check your reservoir or top tanks, as pH can alter as nutrient solution levels fluctuate.

Altering Ph Used To Be A Delicate Process


Altering pH used to be a delicate process, put it has become much easier with the introduction of specific cannabis pH kits to the market. There are even a few kits that adjust pH automatically!

Some old-school hacks we like to use to adjust water pH:

pH up – to make water more alkaline, dissolve garden lime in your water. Take it easy until you find the amount that works for you per litre.

pH down – to make water more acidic, use white vinegar. What? I hear you scream, vinegar! But for real, it works a treat.

While correcting pH, it is a good time to flush your plants out with some of your newly corrected water, helping bring the soil to level.

It is a good idea to do this with oxygenated water prior to the lights going off, giving the plants a night time boost that mimics nature. Taking oxygen in at the roots and creating more root mass.

Outdoor growers and indoor soil growers have an advantage when it comes to pH. They have a greater margin of error. The colonies of microorganisms that form in organic growing matter act as buffers and filters and help keep pH between 6.5 and 7 most of the time.

Nutrient build up isn’t usually a problem when growing organically outdoors either, as rain is the great neutralizer and thieving cannabis trees tend to gobble so much food you usually end up having to supplement the soil anyway.

This doesn’t mean you should be complacent. Although you would need to have some kind of toxic event in your water source to have pH problems outdoors, it can happen. We have seen growers being caught out and suffering as a result.

The moral of the story is always take the time to check on your pH; it is simple to test and easy to rectify when wrong, but it can cause all sorts of havoc if left alone. Don’t get lazy. Check your pH.

Water is a foundation of life. This is no less true for cannabis, which relies on water for a whole array of functions. In our previous blog on water quality, we assessed why water is important, and how pH can affect many aspects of your grow. Today we are going into a bit more detail with ppm and EC. Both are more advanced aspects of cannabis growing that need to be taken into account, and getting your head around it will help push your skills to the max. For the novice, while important, this information is not essential to grow. It is still possible to get great results without it, but it will certainly help!


Don’t be daunted by these technical-sounding terms. Parts Per Million and Electrical Conductivity are two ways of saying the practically same thing. Now, we could get really technical really fast here in comparing ppm and EC, but for the sake of clarity, let’s stick to ppm for the moment.

PPM is a way of measuring the amount of minerals already dissolved in your water, and varies from source to source and place to place. For example, if you have a ppm reading of 100 there are 100 milligrammes per litre of minerals already in your water. Although this is a microscopic amount, the canny cannabis grower knows that plants can only absorb a limited amount of nutrients per day and adjusting for ppm helps get the most from your crops.

Knowing your ppm helps you avoid possible burning by letting you know when to adjust the amount of nutrient minerals you add to your water. Cannabis enjoys 500-600 ppm after cloning, 800-900 ppm when vegetating, and 1000-1100 ppm when flowering. So knowing the mineral content of your water before mixing your nutes can avoid stressing you and your plants. For DWC (hydroponic) growers, it is important to know the condition of the reservoir water, as minerals can deplete as the water level drops – it is a heads-up for you to just top things up as required.

There are many probes, devices and metres on the market all able to measure ppm. The most common is a TDS metre (total dissolved solids). What you go for really depends on your budget, and desire to get technical and nerdy with your grow. Most have a range of 3500, which is all you will ever need for cannabis, but if you like the overkill some will read up to 9999.

Once you have calibrated your TDS metre, turn it on, make sure it is reading zero and put it in the water you want to test – hey presto, there’s your ppm reading. If you are using reverse osmosis water, the reading will be 0 to 10 ppm as it is completely free of minerals.

If you use tap water, your reading should be between 50 and 300 ppm here in the EU as standard.

If your town’s plumbing is old, or you are using well water from limestone strata, you may get a reading of up to 500 to 700ppm because of the mineral build up.

If your water is reading over 500 ppm, you need to do something about it, as it will compete with and lock out the nutrients you actually want your cannabis to uptake. Either you need to get some nutes designed to be used in hard-water areas, or you need to treat your water at home, either through carbon filters, distillation, or reverse osmosis.

How to Measure CE and PPM of Water When Growing Cannabis


Strap your brains in bitches; this is where things get technical.

EC, or Electrical Conductivity, is a measure of the salinity of a water sample.

The theory being that saline water is charged with sodium ions and this charge can be measured by an EC metre, which tells you the conductivity of your water sample – in microsiemens per centimetre. EC works by assuming an ionic conductivity of sodium as .51 microsiemens per centimetre. This is the base charge off which metres calculate conductivity.

If your water is too saline, it can affect your plants in two ways. It can increase the toxicity of sodium at the root ball and increase osmotic pressure at the roots inhibiting nutrient uptake.

PPM measures the overall mineral content of your water, regardless of what those minerals are.

Accurate ppm readings are obtained by gently evaporating the water sample and analysing the remaining residue. Other than sodium chloride most other minerals are hardly present in nearly all naturally occurring water and are not of any real worry. These minerals are usually trace amounts of calcium carbonate, magnesium and micro traces of several other elements.

If you approach your local water authority, they can usually supply you with a mineral analysis of your local water supply.

There are conversions for microsiemens per centimetre to parts per million and back again but most metres do these conversions for you.

Organic soil and outdoor growers have an advantage again when it comes to ppm and EC. The microorganisms provide a buffer that helps protect the plant from fluctuations in ppm or EC and there is a greater margin for error when watering.

Never be complacent, though. Always check your water quality, even from rivers and creeks. You never know what could be washed in upstream during rain that could make your water toxic.

Precise Reading Of The Ppm


Who thinks rain water is neutral? It is a common misconception and is actually mildly acidic. Carbon dioxide dissolves in rain and makes it into a very mild carbolic acid with a pH of about 5.6. Don’t worry, though, once it has sat for a while in a tank or dam or reservoir it releases the carbon dioxide and balances out at 7. Ever noticed how plants grow like mad after rain? That’s why.

When you put your water through a reverse osmosis filter, it makes your water completely mineral free. Never use this water unmodified to flush your plants or as a foliage spray. RO water will strip nutrients from your plants, especially calcium and magnesium. Label your bottles clearly.

Put aerators on your faucets. If filling a container with a hose, make the water froth and bubble to enliven and oxygenate.

In cold climates try and keep your water at 25°C.

There you have it! Things get quite technical, so don’t worry if it takes a while to pick up. Actively working to ensure you have the best water quality you can will help minimise any potential growing problems, as well as give your cannabis what it needs to thrive. The more you know!


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