Which RO System to Buy
Here are my recommendations on RO systems for DWC depending on your grow size
- Aquatic Life 4 stage 1-2 DWC Reservoirs, 240-480W grows (real world is 14 gallons per day)
- Replacement Filters every 6 months
- Express Water 5 stage 5-10 DWC Reservoirs, 2-5 Kw grows (real world 30-50 gallons per day)
- Replacement Filters every 1-2 years, or when ppm exceeds 30
- Inline Carbon Filter – for those with low ppm tap water that don’t need RO
- Replace every 1500 gallons
Note that you need decent water pressure or the RO system may be slower than the above rated numbers.
What is RO?
RO stands for Reverse Osmosis – a water purification process that uses a membrane to separate ions, unwanted molecules and larger particles from your tap water. The first part of determining if you need an RO system for DWC is to measure your baseline ppm. This can be done using a TDS/EC meter. In my experience if your tap water ppm is below ~200, and you have not had any plant health issues, you can likely get away with just using an inline carbon filter instead of a full RO system.
The RO system will bring your water down to 0 ppm, so you will need to supplement with calmag before adding your nutrients.
The cleanest way to hookup an RO system is using a self-piercing saddle valve. Remember that most household RO systems operate at 25% efficiency. Typically for every 1 gallon of RO you’ll have 4 gallons of waste water (can be used for outdoor watering or cleaning). The 1/4″ tubing the comes with the saddle valve is what all of the RO systems below use.
The simplest way to hookup an RO system is using the attached tubing to a faucet or garden hose. Most of the RO systems include these adapters, but if not all you need is a faucet to 1/4″ QC adapter or garden hose to 1/4″ QC adapter.
Stockpiling RO Water (Auto Shutoff DIY)
Most household RO systems produce water at a fairly slow rate. If you leave it filling a container it won’t know when to stop, which could result in flooding. The solution to this is to wire up a solenoid to auto-stop when a pre set water level is reached. This is borrowed from my nutrient mixing tank tek.
Materials needed for Auto-Off Solenoid:
- 12V Normally closed Solenoid 1/4″ Quick Connector
- 12V Power Supply (Universal ones work well)
- Float Switch
The wiring diagram above shows the basic idea. The 12V power adapter causes the solenoid to open. Always use a normally closed solenoid (NC), so that if your power goes out the valve will close automatically. The float switch determines if the flow continues or not. You should also have a water valve after the solenoid so that you can manually close the water off when leaving the system unattended.
You can see my basic design above. The float switch is attached to a bigger piece of grey pipe that slides up and down the white PVC. There is a screw on the grey pipe which I hand tighten to fix the position in place. This allows me to control how many gallons I want the water supply to shut off at.
My container is 45 gallons and was 18″ tall. This made for easy math. Every 2″ I drew a 5 gallon mark
=18 inches / (45gallons/5gallons per line)
=18 inches / 9 lines
=2 inches per line
If you do not care for being able to adjust the level of water you require, this can be done cheaper using a float valve auto shut-off, similar to what is used in the DIY humidifier tek. Just mount to the top of your RO container and click the 1/4″ tubing right in.
If you are grower switching to an RO system don’t forget to pickup a calcium/magnesium supplement such as CALiMAGic. Use 1 tsp per gallon (1 ml/ liter) of water for most applications.
