Survey of the Composition of Water Supplies Used in Glasshouses

Sample bottles and questionnaires were sent to 240 glasshouse growers in 24 counties. A response of 87% was obtained. The water samples were analysed for pH, Ca, Mg, Na, K, P, Mn, O, specific conductivity (SC) and total hardness. Information was obtained from the questionnaire on water source, storage, treatment, presence or absence of algae, use of a boiler for heating and sterilising, and type of feeding system used. Calcium and SC readings fluctuated most and, in general, supplies from wells were hard while those caught as 'roof rainwater' were very soft. The linear correlation between Ca contents and SC readings was 0.91, and the hardness of water was correctly predicted for 157 samples out of 197 by making an SC reading and converting it to ppm Ca using the regression line. Thirty-six percent of samples were obtained from wells, 29.4% from 'mains,' 14.7% from rivers and the remainder from combinations of these or other sources. Supplies which were stored were more likely to contain algae than those which were not. The hose system of feeding was used most frequently. Forty-five percent of growers used boilers, but of these less than one-fifth treated the water. Of the samples not treated 26.5% were classified as moderately hard, 21.0% as hard and 4.2% as extremely hard.