How to add a Water-Save / Piggyback RO Membrane Kit

More water! Faster! That is what many of us want from our RO/DI systems. Less waste water is great too.

Piggyback kits are one of our most-popular upgrades. Not only can they help to make water faster, they can also save your waste water by up to 50%. By adding one or two of our Piggyback kits, you can double or triple your water output and waste less water all at the same time! 

Piggyback (aka. Water Saver Kits) can be installed in 2 different ways: in-series or parallel. 


In-Series (Water Saver) Installation: more water production & reduce waste water by 50%. This is the more-popular of the two installation options. When plumbed in-series, waste water from the first membrane feeds the second membrane. That waste water then produces more product water when it goes through the second (or third) RO Membrane. Depending on the water pressure, output is nearly doubled and the waste water is cut in half. Water pressure will drop by approximately 10PSI after the first membrane, so you will want to make sure you have at last 65PSI for both membranes to be able to function efficiently.  

As it is the waste water supplying water to the second RO membrane, it will have higher TDS than your source/tap water. This higher TDS water will wear out the second membrane quicker than the first RO Membrane. The water produced by the second RO Membrane will also have a higher TDS. For these two reasons, we recommend this installation option when you have good water pressure and a somewhat low TDS (less than 250ppm). 

Adding a third RO Membrane will further increase water output and reduce waste water. However, there will be a 20PSI drop from the first RO Membrane to the third RO Membrane, so a booster pump is recommended. 


Parallel Installation: increase water output, longer membrane life for applications with high TDS water, or lower water pressure. 

The Parallel installation option splits the incoming water two, or three, ways to feed each RO Membrane. As each RO membrane is getting the same quality water, you will not run into the issue where one membrane fouling up quicker than the other. This is especially helpful if the source water TDS is high (over 300ppm). Another scenario where the parallel installation may be preferable is when the water pressure is lower than 65PSI. The Parallel installation option helps to ensure each membrane gets the same amount of water pressure and each membrane produces as much water as possible. This installation option focuses on maximizing water production, maximizing water quality and even RO Membrane wear/life. The disadvantage of the Parallel installation option is that the waste-to-product water ration is not any better than with a single membrane so you are not saving waste water. If 3 RO membranes are being used, a booster pump is highly recommended.  

When a lot of water is being made, it is especially important to keep your RO membranes in tip-top shape. Flushing your RO membrane will help to keep the RO membranes clean and help it last as long as possible. When plumbed in-series, our standard Flush Kit will work. When plumbed in parallel, you will want to select the matching 200GPD or 300GPD Flush Kit to match your system.  

AquaFX Flush Kits

Here are a couple of scenarios comparing the two installation options: 

Scenario 1 - In-Series:  if the source water has a TDS of 200ppm and the RO Membrane is rejecting 95% with a 3:1 waste-to-product water ratio, the first RO Membrane will produce product water TDS of 10ppm. The waste water going to the second RO Membrane will measure roughly 270ppm: meaning water coming out of the second RO Membrane will yield a product water TDS of 14ppm. The 3rd RO Membrane will see a TDS of about 350ppm and produce water measuring 18ppm: with the average of the 3 being 14ppm. A DI cartridge can process about 500 gallons of water @10ppm. At 14ppm, that capacity is reduced to 357 gallons. The end result is that the DI will need to be replaced more frequently. Life of the second and third RO Membrane are also shortened as they are processing water with higher TDS. However, by plumbing the RO membranes in-series and utilizing the waste-water for the subsequent membranes, the waste-to-product water ratio is dropped to better than a 1:1 ratio (producing 2.3 gallons of product water and 1.7 gallons of water from 4 gallons of total water used) saving quite a bit of water. 

Scenario 2 - Parallel: with the same parameters as above, each RO membrane performs the same and will provide product water with a TDS of 10ppm. Your DI will produce 500 gallons of water. However, the waste-to-product water ratio will remain 3:1, so you waste more water compared to the in-series option. As each RO membrane sees the same 200ppm water, their usable life will be the same.  

Adding a Piggyback / Water Saver kit to your RO or RO/DI system is the best way to get more purified water for your aquarium. Understanding the advantages and disadvantages of each installation option will help you to choose the best option for your application.  

AquaFX RO Membranes are made in the USA and offer some of the best rejection rates to give you purer water. We are also available by phone or via email to help answer any questions you may have. 

At AquaFX, we offer Better Filters and Better Service! 

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