Water Quality
All hydroponic/soilless culture systems require sizable quantities of relatively
pure water. The best domestic water supplies and/or water for agricultural
use frequently contain substances and elements that can affect (positively or
negatively) plant growth. Even rainwater collected from the greenhouse covering
may contain both inorganic and organic substances that can affect plant
growth. In many parts of the United States and indeed throughout the world,
water quality can be a major problem for hydroponic/soilless culture use due
to contamination by various inorganic and organic substances.
Therefore, a complete analysis of the water to be used for any type of
hydroponic/soilless culture system is essential. The analysis should include
inorganic and organic components if the water is being taken from a river,
shallow well, or other surface source. When taken from sources other than
these, an inorganic elemental assay will be sufficient to determine elemental
composition and concentration.
Natural water supplies can contain sizable concentrations of some of the
essential elements required by plants, particularly Ca and Mg. In areas where
water is being taken from limestone-based aquifers, it is not unusual for
concentrations of Ca and Mg to be as high as 100 and 30 mg/L (ppm),
respectively. Some natural waters will contain sizable concentrations of Na
and anions such as bicarbonate (HCO3
–), carbonate (CO2
3–), sulfate (SO4
2–),
and chloride (Cl–). In some areas, B may be found in fairly high concentrations.
The Nutrient Solution 73
Sulfide (S–), primarily as iron sulfide, which gives a “rotten egg” smell to water,
is found in some natural waters.
Suggested composition characteristics of waters suitable for use hydroponically
as well as for irrigation have been published. Verwer and Wellman (1980)
established what the maximum mineral concentration would be for water used
in rockwool culture, as shown in Table 7.1. Farnhand et al. (1985) have
established criteria for irrigation water based on salinity, electric conducivity
(EC), total dissolved solids (TDS), and ion content (Table 7.2). Waters et al.
(1972) have set the suitability of water for irrigating pot plants; their data are
given in Table 7.3. Smith (1999) elemental maximums for water for hydroponic
use (Table 7.4). Ideal water-quality guidelines for plug culture and characteristics
of high-quality irrigation water are given in Table 7.5 and Table 7.6.