High pH, high alkalinity water
High pH and high alkalinity water (150+ ppm CaCO3) has the greatest effect on species that require low growing medium pH and are prone to iron chlorosis. Some important greenhouse crops sharing these two characteristics include petunia, calibrachoa, scaveola, bacopa and snapdragon. Irrigating with high alkalinity water tends to increase the growing medium pH because of the liming effect caused by the carbonates and bicarbonates (sources of alkalinity) in the water.
Corrective actions are meant to lower the growing medium pH by using acidic fertilizers, avoiding overliming and in some cases by water acidification. Also, application of an iron chelate fertilizer solution to prevent or correct iron chlorosis is a very effective action.
These corrective actions are meant for the very small group of species listed above. No action would be needed for most greenhouse crops because they are not susceptible to iron chlorosis. In fact, irrigating with this water might help prevent iron and manganese toxicity on marigolds and geraniums and provide supplemental Ca and Mg to crops with a special need for these elements.