Reverse Osmosis System - How to remove scale, toxins and nutrients from tap water
By Robert B.
Drinking water supplied to urban dwellers normally has a nitrate value of 0.4 to 0.8 EC and this is a good output value to mix water with a nutrient solution for marijuana plants. However some people use their own water pumps to draw irrigation water with a nitrate level of up to 1.5 EC. You can add virtually no nutrients to water with this concentration to irrigate plants. If you do not have enough rainwater available to be used to dilute tap water, you will really be in trouble.
However this should be no impediment to growers. Special systems are used to reduce the nitrate level of water to 0.6 EC (please note that a simple reverse osmosis system is not sufficient for a level of 1.5 EC.) These systems work like a normal reverse osmosis unit for aquariums but can be purchased from the sanitary area of a do-it-yourself store. Water is pressure-pumped into the system and channelled over a couple of membranes, through which pure water goes through, whereas water containing nitrate is dumped. Water is not 100% pure but less wastewater will be produced.
[caption id="attachment_9025" align="alignnone" width="800"]
This is a small reverse osmosis unit for aquariums available at a price of 115€, with a purification capacity of 70 litres of water per day. It suffices to fit it to a three-bar water supply system. The water passing beyond the membranes is dumped, and the water channelled through the membranes is collected.[/caption]
If nitrates in tap water are unsuitable for plants and you cannot add a sufficient quantity of cannabis fertiliser to irrigation water, then it would be better for the plants to be fed with clean nitrate-free water generated by a reverse osmosis system. We thought about it and, for six months, we mixed irrigation water with nitrate-free water to water our plants. The output nitrate value was 0.6 EC. We could not find any difference in the plant growth and in the quality and quantity of the harvest. Plants do not necessarily need a good fertiliser and a small proportion of unusable nitrates do no harm. During the blooming season, instead, they need a specific fertiliser dose for them to absorb a large quantity of a good fertiliser. However they use it only partially as most of it remains in the substrate or is drained away. If water from the tap has a value of 0.4 to 0.8 EC, this is good enough and no better water is required. So you can avoid wasting four litres of water for each litre of pure water.
[caption id="attachment_9026" align="alignnone" width="800"]
This shows a water tank with a lid. The lid has a free corner to which the cable of the float is attached. If pressed a little downwards this cable will lift the lid. If the lid falls, the float switch will continue to convey electricity to the solenoid valve, and water will be supplied to the reverse osmosis system. In this case the cable for the purified water was simply extended, and water is automatically pushed into the tank. If the float fails to reach a vertical position, it will not stop supplying power to the solenoid valve and the tank will overflow.[/caption]
As an exception, self-contained systems are also available that work without drainage and a fresh nutrient solution can always be refilled. With these systems, however, fertilisation should be carried out with the utmost care. Nitrates that cannot be assimilated by plants will accumulate and pollute the root system. In this situation you should probably use nitrate-free water to which a nutrient solution should be added.
If you do not use nitrate-free water for irrigation, you will indeed need it for air humidifiers. Limy water should be avoided for all types of humidifiers, including ultrasonic humidifiers; otherwise lime scale will easily spoil them. You will notice a lime film on the surface of your humidifier if you are using water with a high lime concentration.
Reverse osmosis systems should never get dry. If the system is not used, the inlet hoses should not deliver air to the membrane compartment but rather be bent upwards.
Most of the time, the water tap of the reverse osmosis system is controlled manually, which frequently causes the water in the collecting tank to overflow. The tank can be placed in a bathtub or close to a drain. Another option is purchasing a solenoid valve and a float ball switch from a do-it-yourself store. The float should be fitted with 4 wires (those with only three cables are designed to pump water out of tanks). The grower should check when the tank is full, as this will cause the solenoid valve to trip, which will shut down the reverse osmosis system.
If the float switch remains suspended, it continues to convey current to the solenoid valve, which will continue supplying water to the reverse osmosis system. The system will then be powered off, if the float ball is brought to a vertical position, and water will not flow out of the tank, which will remain full. In our experiment we used a soundproof water pump to supply purified water to a Mist&Cool humidifier and spray water onto plants during the blooming phase. By a time relay, the pump was set to run for 20 sec. followed by a 5-minute pause to prevent the Mist&Cool to swamp the system.
Later, a large ultrasonic humidifier was purchased to which water was supplied through the water tank installed above. This prevented the delicate membrane from being spoilt by lime scale and air was moistened even better than it was before (unfortunately ultrasonic humidifiers absorb more power than Mist&Cool humidifiers do). In doing so, water was not deposited on the surface, but the aerosol fog was rather spread in the air. The desired air humidity can be freely selected through a hygrostat. For this reason ultrasonic humidifiers are better devices for air humidification, however they should be mounted in the direction of incoming air. Small compact units with a four-litre tank could be hung at the same height as reflectors or above them.
[caption id="attachment_9028" align="alignnone" width="800"]
This shows a solenoid valve, it must be connected to the float. The phase line is further connected through a lamp terminal to the solenoid valve, whereas the earth line is connected to the float. The earth line is connected to the brown cable of the float, and returns through the black cable. If water needs to be pumped out of the tanks, the earth should be connected to the blue cable, which will empty the tank – unfortunately this is not perfectly visible. The earth line is conveyed to the solenoid valve through the black cable of the solenoid valve.[/caption]
The advantage we found in this installation with a float and a solenoid valve is that you do not have to worry about anything. The tank with clean water is always full and the supply of water initially to the Mist&Cool and then to the ultrasonic humidifier is uninterrupted.
This is a small reverse osmosis unit for aquariums available at a price of 115€, with a purification capacity of 70 litres of water per day. It suffices to fit it to a three-bar water supply system. The water passing beyond the membranes is dumped, and the water channelled through the membranes is collected.[/caption]
If nitrates in tap water are unsuitable for plants and you cannot add a sufficient quantity of cannabis fertiliser to irrigation water, then it would be better for the plants to be fed with clean nitrate-free water generated by a reverse osmosis system. We thought about it and, for six months, we mixed irrigation water with nitrate-free water to water our plants. The output nitrate value was 0.6 EC. We could not find any difference in the plant growth and in the quality and quantity of the harvest. Plants do not necessarily need a good fertiliser and a small proportion of unusable nitrates do no harm. During the blooming season, instead, they need a specific fertiliser dose for them to absorb a large quantity of a good fertiliser. However they use it only partially as most of it remains in the substrate or is drained away. If water from the tap has a value of 0.4 to 0.8 EC, this is good enough and no better water is required. So you can avoid wasting four litres of water for each litre of pure water.
[caption id="attachment_9026" align="alignnone" width="800"] This shows a water tank with a lid. The lid has a free corner to which the cable of the float is attached. If pressed a little downwards this cable will lift the lid. If the lid falls, the float switch will continue to convey electricity to the solenoid valve, and water will be supplied to the reverse osmosis system. In this case the cable for the purified water was simply extended, and water is automatically pushed into the tank. If the float fails to reach a vertical position, it will not stop supplying power to the solenoid valve and the tank will overflow.[/caption]
As an exception, self-contained systems are also available that work without drainage and a fresh nutrient solution can always be refilled. With these systems, however, fertilisation should be carried out with the utmost care. Nitrates that cannot be assimilated by plants will accumulate and pollute the root system. In this situation you should probably use nitrate-free water to which a nutrient solution should be added.
If you do not use nitrate-free water for irrigation, you will indeed need it for air humidifiers. Limy water should be avoided for all types of humidifiers, including ultrasonic humidifiers; otherwise lime scale will easily spoil them. You will notice a lime film on the surface of your humidifier if you are using water with a high lime concentration.
Reverse osmosis systems should never get dry. If the system is not used, the inlet hoses should not deliver air to the membrane compartment but rather be bent upwards.
Most of the time, the water tap of the reverse osmosis system is controlled manually, which frequently causes the water in the collecting tank to overflow. The tank can be placed in a bathtub or close to a drain. Another option is purchasing a solenoid valve and a float ball switch from a do-it-yourself store. The float should be fitted with 4 wires (those with only three cables are designed to pump water out of tanks). The grower should check when the tank is full, as this will cause the solenoid valve to trip, which will shut down the reverse osmosis system.
If the float switch remains suspended, it continues to convey current to the solenoid valve, which will continue supplying water to the reverse osmosis system. The system will then be powered off, if the float ball is brought to a vertical position, and water will not flow out of the tank, which will remain full. In our experiment we used a soundproof water pump to supply purified water to a Mist&Cool humidifier and spray water onto plants during the blooming phase. By a time relay, the pump was set to run for 20 sec. followed by a 5-minute pause to prevent the Mist&Cool to swamp the system.
Later, a large ultrasonic humidifier was purchased to which water was supplied through the water tank installed above. This prevented the delicate membrane from being spoilt by lime scale and air was moistened even better than it was before (unfortunately ultrasonic humidifiers absorb more power than Mist&Cool humidifiers do). In doing so, water was not deposited on the surface, but the aerosol fog was rather spread in the air. The desired air humidity can be freely selected through a hygrostat. For this reason ultrasonic humidifiers are better devices for air humidification, however they should be mounted in the direction of incoming air. Small compact units with a four-litre tank could be hung at the same height as reflectors or above them.
[caption id="attachment_9028" align="alignnone" width="800"] This shows a solenoid valve, it must be connected to the float. The phase line is further connected through a lamp terminal to the solenoid valve, whereas the earth line is connected to the float. The earth line is connected to the brown cable of the float, and returns through the black cable. If water needs to be pumped out of the tanks, the earth should be connected to the blue cable, which will empty the tank – unfortunately this is not perfectly visible. The earth line is conveyed to the solenoid valve through the black cable of the solenoid valve.[/caption]
The advantage we found in this installation with a float and a solenoid valve is that you do not have to worry about anything. The tank with clean water is always full and the supply of water initially to the Mist&Cool and then to the ultrasonic humidifier is uninterrupted.
