One of the most common questions that I get from beginner hydroponic gardeners is:
Can you use tap water for hydroponics?
It’s a good question! When you’re just starting out, you want to get up and running quickly. Your other options for water are all more complex than just using water straight out of the tap:
- Distilled (costly)
- Reverse Osmosis (costly, wastes water to produce)
- Filtered (requires extra gear)
It’s no surprise that people want to use tap water for their hydroponic gardens.
But is it safe for your plants?
To answer this, we have to look at what happens to our water before it comes out of our tap. In terms of plants, one of the most important considerations is water chlorination.
What Is Water Chlorination?
Adding chlorine or hypochlorite to drinking water in order to kill bacteria and other microbes. Chlorine is extremely toxic to these small organisms and water chlorination’s primary purpose is to destroy any diseases that could be transmitted in our drinking water.
That doesn’t sound too good for our plants and the various beneficial bacteria that live in our nutrient reservoir, does it? It’s not…but there’s a secret.
Chlorine can break down if you leave your tap water out in the sun.
It’s commonly quoted that chlorine will “evaporate” from water if you leave it out, but that’s not what’s going on. The water needs to be exposed to UV rays from the sun in order to begin the breakdown process of the chlorine.
How Long to Leave Tap Water in the Sun?
In order to break down nearly all of the chlorine in your tap water, you’ll need to leave it out for about 24 hours. Make sure you over-fill your reservoir to avoid losing too much water due to evaporation.
Chloramine: Another Potential Threat
Chlorine isn’t the only additive you need to worry about. Sometimes tap water is disinfected with chloramine. If you’re growing in an aquaponics system then it’s especially important to rid your water of chloramine, as it’s toxic to fish.
What Is Chloramine?
Chloramine is a combination of chlorine and ammonia that’s used as a water disinfectant much like regular chlorine. The difference is chloramine lasts much longer and is harder to break down.
This disinfectant is a lot harder to get out of your water, but it’s still possible. The two easiest ways to make sure your water is chloramine-free is to run it through an active carbon filter (like a Brita filter) or use Campden tablets.
Campden Tablets can remove chloramine from your tap water
If you don’t want to use those methods, you can boil your tap water, but it’ll still take quite a while, so I don’t recommend this water.
Finally, you can also apparently use a chemical called sodium thiosulfate to break down both chlorine and chloramine, which is a very common tactic for those who own aquariums.
One Final Consideration: Tap Water PPM
Now that you know how to rid your water of chlorine and/or chloramine, you probably think you can rest easy.
Not so fast.
The last thing to consider is what ELSE besides pure H2O is in your water. This is measured by the parts per million (PPM) of your tap water.
You may have heard of the terms hard water and soft water.
Hard water creates that nasty buildup on your showerhead.
These refer to the amount of minerals in your water. Hard water contains more minerals and is what leaves that nasty buildup on your shower head if you’re unlucky enough to live in an area where you have hard tap water.
How Hard Water Affects Plants
When you have extremely hard water, your plants can be at risk due to an overabundance of minerals that they only need in small amounts. Some of the culprits here are calcium and magnesium, both minerals that your plants need to thrive…but they don’t need as much as the macro nutrients plants need.
A general rule of thumb is that water in the 200-300 PPM range is OK for your plants. Anything higher and you may run into issues.
I like to test my water with a Bluelab PPM meter, which I also use to measure the PPM of my nutrient solution when growing plants as well, so it serves a nice double duty.
So to answer the original question…can you use tap water for hydroponics?
Yes, yes you can – if you treat it properly beforehand!
- If it’s chlorinated, make sure to leave it in the sun for 24 hours
- If it’s chloraminated, use a filter or Campden tablets
- If it has a high PPM, consider running it through a filter or mixing in distilled or reverse osmosis water to dilute the concentration.
If you’re interested in reading further about chlorine and chloramine, please check out this paper on removing both substances from brewing water.