How to run a hydroponic drain to waste system?

drain to waste hydroponics

With all the different types of hydroponic systems out there, drain to waste has to be the favorite. The main reason most gardeners like it so much is the method of providing plant nutrients. In the other hydraulic systems (deep water culture, ebb and flow, nutrient film technology, and aeroponics) the nutrients are returned to a reservoir and recycled through the system.  The deep water culture or DWC uses a bucket, water, air stone, and nutrients, and the roots of the plants grow in the bucket and consume the nutrients you want. The same goes for the other systems. The roots emerge or are constantly watered as they absorb the nutrients from their reservoir, the plants eat, by absorb the nutrients that are available.

When it comes to watering your plants, of all existing combinations and variations, we can summarize them in two principles. Each has its pros and cons. In addition, the advantage of one producer is the disadvantage of another, depending on the circumstances. There are only two ways to water your plants, using a recirculation system or a drain-to-waste approach.

What is drain-to-waste (DTW) or run-to-waste (RTW)?

DTW or RTW is the term used for a hydroponic system where nutrients are not recycled. Run-to-Waste systems are usually used as an inert medium with liquid retention comparable to that of soil. That is, the waste medium retains a high degree of moisture for a long period of time. As a result, food is smaller than and not as frequent as food in a recycling system.

 In the drain to waste system, the plants receive a regulated dose of water and nutrients at such a rate that a small amount of water or nutrients is discharged from the medium. The excess water and nutrients can then drain in some form of the catchment area, away from the reservoir. The waste is never returned to the plants. Since nutrients are not recycled, there are some clear benefits to the waste system:

Why run drain to waste?

Drain to waste system provides more control over your plants and helps prevent disease, a common concern is that the system is wasting too many nutrients due to the excessive amount of waste that drains. This is simply not the case. A clear drain to waste system wastes only 10-15% of the nutrient solution that is supplied as run off.

An example of this is the following – a particular garden uses 5 gallons of water to feed all the plants, the waste runoff will be only 1/2 to 3/4 gallon of solution. When using Drain to Waste with coir, soil, or rock wool, the frequency of watering is kept to a minimum, usually once a day or once every day. Why would I “Drain to Waste?

The three main reasons for performing “Drain to Waste” are as follows:

Less chance of root rot

The most common root rot problems arise from pathogens that produce spores as a way to spread their colonies and infect more plants. The disease starts in a plant (usually the weakest) in the garden and uses this plant to produce more spores (in an attempt to infect more plants with larger and stronger colonies). In a recirculation system, the spores generated by this plant run off the plant and accumulate in the main tank where they produce and masse with the water supply and then infect all the plants in the garden during the next and consecutive irrigations. With “Drain to Waste” this cannot happen because the water leaving a particular plant goes to a drain and does not return to the “main tank”. Therefore, no trace can infect a reservoir.

It always give your plants a fresh nutrient-rich solution

In a Drain to Waste tank, the nutrient-rich solution feeds the plants and the runoff get to the bottom of the plants and is drained out. This ensures that the plants receive only fresh non-recirculated nutrients every time. The difference between the “Drain to Waste” and “Recirculating” reservoirs is as follows: In a recirculating reservoir, the nutrient solution starts completely according to the original recipe in the bottles.

As watering or feeding continues and plants feed on the nutrient solution throughout the week, the solution loses important minerals for the plant’s unique nutritional needs. This also causes precipitation to form when certain minerals (now in new molecular arrangements) become trapped and fall out of the solution. Now the original recipe is no longer intact. This is not the case with “Drain to Waste”. The recipe remains intact and the plants receive their full nutritional requirements at all times. This ensures healthier, stronger, and faster growth.

The ability to make Flushes and Drenches

Flushes are important in a coco-based or rock wool medium. The flushes make it possible to readjust the medium, as well as the extraction of unwanted nutrients in the plants themselves. Flushes can be crucial for good, healthy plant growth. Under normal conditions (recirculation system), a flush removes the salts from the medium and from the plant, sucks them into the reservoir, and then pumps them back to the plants over and over until the reservoir is empty and the cycle is repeated a few times. With “Drain to Waste” this is not necessary. We can perform a flush to waste. All salts and excess minerals are removed from the plants and are truly flushed away.

Drenches are also another interesting feature of the Drain to Waste systems. For example, products such as Gnatrol are made to be used in a soil system and not designed for a recirculating hydroponic system. With a drench, you can fill the tank with a particular product and run it through the system once or twice and then flush or replace the tank and go back to the normal feeding regime and feed it normally. There are many products that are made for drench. Alternatively, it can be drench by pouring over the tops of the plants and then flush.

Other reasons why Drain to Waste is a better overall system option:

  • Most large farms use drain to waste
  • PH doesn’t fluctuate that much
  • The system itself stays cleaner
drain to waste advantage

How to perform a drain to waste

Flushing is integral to growing happy, healthy plants. Flushing a system and the plants remove excess salts that have accumulated over time. Flushing will also help restore a uniform CEC (cation exchange capacity) balance to moderate levels. Most mediums retain and release salts back into the root zone over time, or attract more salts to the salts that are already beginning to form, promoting an ever-downward spiral to towards nutrients lockout. In other words, for starters, the more salts in a medium, the greater the potential to attract more and more salts, until the plants eventually cannot extract any water (or nutrients) at all. Blockage can easily be prevented by flushing from time to time. Some mediums need to be washed more than others.

How to flush?

Flushing is quite easy to do. The first thing you need to do is, drain your tank and then fill it with fresh reverse osmosis (or purified) water. Add a flushing detergent such as Clearex or pH to the solution (always pH, never forget pH, always pH last, just before watering your plants). Allow at least 3 times the normal amount of water to run through the plants.

For example, if your plants normally use 3 gallons of water per watering, be sure to flush 9 gallons of water through them. (If using a recirculation system, do this for at least 2 irrigations). Then drain the reservoir and refill the nutrient solution as usual. You can wait to feed them until the next scheduled time or feed them immediately.

What is the Difference between a recirculation system and a drain to waste system?

In recirculation system and drain to waste there is a big difference between in the two systems, they are both excellent and can be used to grow flowering hydroponic crops.

The recirculation system and the drain to waste system are somewhat related to each other, except for one main aspect, which is how the nutrient solution discharge is disposed of. The real question is which system is best suited for your situation. But to answer this question, you first need to know how both systems work.

A recirculation system may be best for large-scale hydroponic farms where multiple plants grow together. On the other hand, the drain to waste system may be more suitable for growing hydroponic plants on a small scale.

Recirculation system

One of the most important features of a recirculating DWC is that the entire unit system is piped and connected to the main nutrient reservoir. The run-off nutrient solution will go from the DWC system to the nutrient reservoir through connected tubes.

The nutrient reservoir will collects and mixes the solutions from all DWC hydroponic recirculation systems. When it reaches the nutrient reservoir, the pH and ppm of nutrients are retested and returned to normal levels. In addition, any drop in the water level is topped up.

Drain to waste system

On the other hand, in a drain to waste system, the run-off nutrient solution is simply flushed away by draining it. There is no recycling. The nutrient solution is checked regularly and flushing should be done in time to ensure there is no build-up of salts.

Advantages of a recirculation system

Reduce nutrient consumption

Nutrients are added to the nutrient reservoir from time to time when the ppm falls below a certain level. Nutrient ppm levels usually need to be stable to ensure healthy crop growth rates.

The recirculation system tends to prevent a large amount of nutrients from running out and wasting. Instead of flushing your hydroponic system and wasting a lot of nutrients, you recycle the pre-existing nutrients in the nutrient solution.

Water recycling

Reducing your water usage is one of the major benefits of using hydroponic systems. In fact, hydroponics can save up to 80% of water usage compared to soil.

Using a recirculation system saves a significant amount of water that would otherwise be disposed of with each flush. This can significantly reduce your monthly water bills and if you use hydroponic systems extensively, you can save a lot on the monthly expenses.

Can be widely used

In my opinion, the widespread use of hydroponic systems is key to making hydroponics farming businesses as profitable as growing them on soil. By connecting all your DWC systems via pipes to a large central nutrient reservoir, you save a lot of work and energy.

Imagine having to test the ppm and pH of 50 tanks of nutrient solution every day, quite a tiring job, right? If you are using a recirculation system, you do not have to process all of this. You just need to keep an eye on a central reservoir every day, that’s it.

Disadvantages of a recirculation system

Spread of water-borne diseases easily

There is a major drawback to having all of your plants linked together into a single nutrient reservoir, namely the easy transmission of water-borne diseases.

When a single plant is infected with a particular disease in a normal runoff to waste the DWC system, it can be isolated from other surrounding plants to reduce the risk of spreading the infection. Unfortunately, this cannot be done on a recirculating DWC system.

You must understand that there is an associated risk of rapid disease transmission if you choose to use the recirculation system as your primary DWC cultivation method. You can reduce the risk of contamination of your entire hydroponics by splitting them into different recirculation systems with different nutrient reservoirs.

Clogged pipes

By using a recirculation system with its complicated pipe network, you have a greater chance of these pipes becoming blocked for various reasons.

When using a recirculating system the pipes can become clogged for a variety of reasons, such as the growth of algae and bacterial biofilms. In addition, the build-up of dead plant roots can also increase the likelihood of pipes becoming clogged.

Growing a limited variety of plants

Different plants require different levels of ppm and pH to thrive. Previously this was easy with the drain to waste system, but now, with a recirculation system, it has become more difficult to do this.

If you choose to use the recirculation method, you should grow plants with similar ppm and pH requirements together in the same system. Growing different plant species requires more than one recirculation system for each plant species to thrive.

Advantages of drain to waste system

Less chance of clogging the system

Another advantage of using the drain to waste system is that there are no lines or emitters involved in the system; this will likely save you a lot of headaches, as pipes often get clogged in systems when using the recirculation method.

Less salt accumulation

The drain to waste method relies heavily on draining all of the nutrient solutions every time we flush the system. This process significantly reduces the risk of salt build-up. A high concentration of salts can result in a nutrient lockout that can seriously damage your hydroponic plants.

Less transmission of waterborne diseases

One of the advantages of a drain to waste DWC system is that the nutrient solution is not connected to other systems.

Having a drain to waste system, separates each DWC system from other systems within the same grows space; This limits the spread of waterborne diseases that can be transmitted through the nutrient solution to reach the other plants you are trying to grow.

Better pest control measures

Imagine you have a plant pest within a DWC recirculation system. It would be a nightmare for you to figure out how to use pest control chemicals in the nutrient solution without other plants in the same system being able to absorb it.

This is no longer the case for the drain to waste system. Having the nutrient solution separately for each DWC system has the great advantage of limiting the use of pest control chemicals to only infected plants.

Disadvantages of drain to waste system

Increased in water consumption

When draining out all nutrient solutions, each time you flush the system a large amount of water is wasted every month. Water efficiency is one of the main benefits of hydroponics and losing it will make me have doubts about the viability of hydroponics over the soil.

Wasting of nutrients

The drain to waste system tends to waste a large amount of nutrients every time a flush needs to be carried out. This nutrient cost will increase your expenses every month, and growing hydroponically on a large scale can cut your profit margin significantly.

drain to waste disadvantage

How to test the runoff coming out of your drain before it reaches the reservoir?

By testing the runoff coming out of your drain before it reaches the reservoir (after a flush is performed), you can see where the pH and TDS (ppm) of the medium rest. Ideally, any amount of water that goes in should be the same as the water that comes out.

For example: the fresh water flush solution that goes in has a pH of 6.0 and a TDS of 0 – 50 ppms (R.O / purified water). The pH of the outgoing drain water should be 5.8 – 6.2 (0.2pH in both directions). The TDS of the water coming out must be within 50 -100ppms (50ppms outside the incoming fresh water coming in).

How to adjust the pH or ppms to equalize the incoming water?

If the ppm of water leaving the drain is greater than 50ppms of water entering the reservoir (Example – 50ppms entering, 100 ppms leaving), then continue flushing until the ppms drops to the appropriate level. If the pH of the flush solution going in and the pH value going out (of the runoff that is collected in the drain) match (at 6.0 in our example), then you’re fine. If the pH does not match the pH of the solution coming out of the drain, then we have to work on the incoming solution until the pH that is coming out matches.

Returning to our example, the incoming pH is 6.0, let’s say the outgoing pH is 7.0; so the average should be around 8.0. For example, if the entering pH is 6.0 and the leaving pH is 5.5, then the medium is around 5.0. So to correct the pH in the first example (the entering pH is 6.0 and the leaving pH is 7.0), one would have to lower the pH of the solution entering the system to 5.0 or even 4.5 and run a fair amount of water into it and test the drain until the water coming out is the pH we want it to be (in this example, it would match the original water coming in at 6.0). Once the pH of the water coming out (through the drain) matches the water solution coming in, a final test is needed. Flush again with the water that comes in (in our example, pH 6.0) and make sure it is aligned and equal to the pH of the water that comes out.) This last step is necessary because the water that is out is not necessarily where the actual medium is. Once the pH of the incoming water matches the pH of the outgoing water, it is done and the medium is “ready”.


By using a drain to waste system, it will provide more control over your plants and helps prevent disease. Also If you can do it right, you will enjoy the extra time off and the additional 15-20% savings that recirculating irrigations provide. On the contrary, when something goes wrong, it goes wrong very quickly. In that sense, the drain is much more forgiving. If you want to grow hydroponically it would be great if you consider using the Drain to Waste method for consistent results and strong, productive plants.

Lindsey Glenn

I've been learning about gardening since 2015, helping friends and family to grow their trees. I am passionate about trees and love sharing everything I learn about them.

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