Water is the foundation of all hydroponic systems. It is very important to know the quality of the water being used because most water already contains various minerals which can effect the pH stability of your nutrient solution as well as the availability of the nutrients for absorption by plants.
How important is water quality in growing?
Water containing excessive calcium and magnesium (ie. "Hard-Water") can cause serious problems. If the dissolved salts in your water supply measure 200 ppm or more, we strongly recommend that you obtain a water analysis to determine calcium content. Excessive calcium is the main factor in determining if your water is hard. If an analysis of your water supply reveals that the calcium content of your water supply is greater than 70 ppm (mg/liter) you should consider purchasing a reverse osmosis water filtration system to filter your water.
Is chlorinated water a problem?
The most common issue regarding tap water and hydroponics is chlorine. Many growers don't realize that chlorine is a micro-nutrient required by plants in extremely minimal quantities. Chlorine is highly volatile and will evaporate from tap water within a day or sooner if the water is aerated. Because plants are able to absorb it, they wind up taking in far too much from unfiltered tap water resulting in diminished growth due to poor root health. The micro-flora and micro-fauna living in the root zone are very important for healthy vigorous plants and high yields. Don't let chlorine kill the good guys!
Chloramines are chemical compounds of ammonia and chlorine that are also used as municipal water supply sanitizers. Chloramines do not evaporate from water the way chlorine does and many water filters which remove chlorine cannot remove chloramine. The effects of chloramine on your garden are even more detrimental than chlorine. If you are concerned your tap water may contain chloramines, have it tested. To avoid problems caused by these chemicals, consider an investment in a water filter or reverse osmosis machine and make sure it takes out both chlorine and chloramine. The improvement in plant health can be considerable which translates to a substantial increase in harvest quality and quantity.
Oxygen and Roots?
Plant root systems need oxygen for aerobic respiration, an essential plant process which releases energy for root growth and the uptake of nutrients. In a deep water culture hydroponic system, it is absolutely crucial to have adequate oxygen levels because roots are submerged. For optimal growth it is recommended to have 1 liter per minute of air pumped into each gallon of nutrient solution. Therefore a 100 gallon reservoir would require a 100 LPM air pump for maximum oxygenation. In every other hydroponic application it is only required to oxygenate the solution enough to prevent it from becoming anaerobic, which means much less air is required. Generally if you have good movement in the solution and the majority of the surface of the solution is broken with bubbles, your plants will do fine. This can be achieved with a simple fish tank pump and air stones.
What about water temperature?
As the temperature of your nutrient solution increases, the less your nutrient solution holds dissolved oxygen. The oxygen content of a fully aerated solution at 10°C (50° F) is about 13 ppm, but once the solution warms up to 20° C (68° F) the oxygen content drops to 9 – 10 ppm. By the time the solution has reached 30° C (86° F), then oxygen content levels are only at 7 ppm. We recommended not exceeding 76° F in your nutrient solution (ideal temp is 24° C or 70° F) in order to keep oxygen dissolved and available for plant roots.