Depending on the quality and hardness of your local area's tap water, you may want to opt for a Reverse Osmosis (RO) Water Filtration System.
Tap water often has many dissolved solids in it, measured in PPM (parts per million), and the amount of these solids vary depending on how your local water department/district treats their water. You can typically find your local water quality report on your local water department's website, but to ensure accuracy, you will probably want to test your water with a TDS (Total Dissolved Solids) tester. TDS testers are also useful for measuring your water after adding nutrients. Most of these testers are extremely easy to use, can be calibrated for accuracy, and they usually display their readings in PPM. High PPM water is most commonly referred to as 'hard water'.
Is Reverse Osmosis Purified Water Really Necessary for Hydroponics? via Everest Fernandez on YouTube
Tap water with a high PPM can cause a number of issues with your grow. In areas with a very high PPM, and even for those without, a reverse osmosis system will ensure your water is as pure as possible so that you are in complete control of what your plants are consuming!
Reverse Osmosis is a water treatment and purification process that leaves your water with a near-zero PPM, removing most minerals and solubles from your water. More specifically, the water is forced through a semipermeable membrane that stops the dissolved solids from also passing through. This gives you a clean baseline to add in your chosen nutrients to your water, ensuring your plants are getting only what they need. It is important to note that there are some useful minerals in the water that the filter will also remove, such as calcium and magnesium. If you're going to be using RO water for your plants, we also recommend using a calcium and magnesium supplement when feeding them. General Hydroponics CALiMAGic is great for exactly this purpose!
While you can buy jugs and visit a local RO vending machine to fill them, many experienced growers instead opt for installing reverse osmosis systems in their home. Having to constantly go out to refill your water jugs at an RO water filling station can become quite the inconvenience, especially as your plants mature during the flowering stage, and even more so when using smaller pots (1-3 gallons).
Reverse Osmosis Water Filtration units can be easily connected to many home water systems, often conveniently under an existing sink! This will allow you to have access to tap or RO water at your choosing.
Video about Reverse Osmosis systems and installation via HonestReviews on YouTube
If you also use humidifiers in your grow room or just around your home, installing a reverse osmosis system has the additional benefit of allowing you to put truly clean water into them. This will allow the humidifiers and their filters (if equipped) to last much longer by preventing scale buildup (from the dissolved solids). Scale and mineral deposit buildup are breeding grounds for bacteria. Bacteria that you surely don't want in your grow tent, or in the air you're breathing!
Here are some of the best Reverse Osmosis systems available today:
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