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In general, proper supply water contains a low sodium content. If you have a soil-bound cultivation, often a sodium content of 0.5 mmol/l is used. By contrast, the sodium content in case of non-salt sensitive cultivations is allowed to be higher. Proper water in general has a pH-value between 4.5 and 6.0. If a lower pH-value is used, then there is a chance that the substrate and the roots will get damaged. Too high values on the other hand, may lead to a reduced availability of trace elements. The presence of bicarbonate in the water ensures that the pH in the substrate increases. Therefore, it is hard to direct the pH-value in the root environment. For this reason, it is important to neutralize the major part of bicarbonate by use of acidic fertilizers. 

Tip: the quantity mmol/l of bicarbonate equals the quantity mmol/l of nitric acid. 

The pH-value of the water can be measured by use of a pH meter. The measuring of the pH-value of the water is done by following step-by-step plan: 

1. Put the solution to be measured in a clean beaker or measuring glass and determine the temperature.
2. Rinse the probe of the meter with demineralized water and clean it with a tissue. Then place the probe in the solution to be measured and stir for a moment.
3. Set the temperature of the solution using the left rotary knob on the meter.
4. Wait 1 minute until the probe is stable.
5. You can now read the pH-value of the water.
6. Finally rinse the probe again with demineralized water and place it back in the meter holder. 

Please note: there must always be some quantity of Probe care present in the holder, as this ensures the preservation of the probe. If the probe is connected, the meter should indicate a pH-value of approximately 4. If the pH is higher than 5, then replace the Probecare in the tube. It is important to regularly calibrate the pH meter.

The pH-value of water may vary per cultivation in substrates or different soil types. Below, the guidelines per type of cultivation are shown.

Soil type	Guidelines	pH-value
Substrates	Put a sample in a well cleaned pot; For recirculation systems the outgoing water can be sampled; In case of Rockwool substrate and synthetic foams, take samples in approx. 20 places	< 4,5 too low 4,6 - 5,3 fairly low 5,4 - 6,1 normal 6,2 - 6,9 fairly high >7,0 high
Peat substrates and potting soil	MMeasure a mixture of 1-part volume of peat/potting soil and 2-part volumes of demineralized water. After shaking of the mixture, the pH-value can be measured directly.	< 3.9 very low 4.0 - 4.7 low 4.8 - 5.5 fairly low 5.6 - 6.3 normal 6.4 - 7.1 fairly high >7.2 high
Greenhouse soil	pH-values in greenhouse soil is more difficult to measure because these are dependent on the carbonated lime content, organic matter content and the way in which the deposition took place. For that reason, there are some guidelines for certain soil types.	A. Sand pH 5.0 - 5.4 low 5.5 - 5.9 fairly low 6.0 - 6.4 normal 6.5 - 6.9 high B. Clay 5.5 - 5.9 low 6.0 - 6.4 fairly low 6.5 - 6.9 normal 7.0 - 7.4 high C. Peat 4.0 - 4.4 low 4.5 - 4.9 fairly low 5.0 - 5.4 normal

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