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The quality of your water is extremely important for good culture.  In nature plants are drenched by rain water. Rain water results from evaporated water and unless it is heavily polluted (like acid rain), that water is very pure.
Rain water is slightly acidic with a PH factor of 6.4 to 6.8.
Tap water is usually quite acceptable.
Well water is acceptable if its content in mineral salts is below 120.  Hard water (water with mineral contents above 120 PPM) will create hard deposits on the leaves of plants.  This may clog the pores on the leaves of plants and reduce perspiration.  If your water is hard it may be beneficial to periodically (once to twice a year) clean the leaves with distilled water.
Be careful with water that was softened.  There are 2 basic products for softening water: salt and potassium chloride.  Salt adds sodium to the water and, over the long term,  this can be deadly to your plants.  Potassium chloride will not harm the plants.
The best water is water processed through a reverse osmosis system which will remove most of the minerals from the water. Our well water has over 1,000 PPM (or TDS - Total Dissolved Solids) of minerals in it (calcium, ...).  We soften it first then we process it with a reverse osmosis (R.O.) system.  The processed water has a mineral content of less than 20 PPM. (Note : if you use an R. O. system then softening the water with salt is fine because the R. O. process will eliminate practically all the sodium).
A small home R. O. system producing 30 gallons of water per day costs from $ 150 to $ 300 (Nature’s Way - 800-780-2320). Nature’s Way offered these systems on sale in September for $ 119 instead of $ 142.50 and $ 279 instead of $ 329.00.
I am not familiar with Nature’s Way system. Our commercial system can produce 1,500 gallons per day. The processed water is stored in 1,000 gallon tank and must be pressurized before we are able to use it.  I just mention this to make you aware that you might need something to storing the water if you consider an R. O. system.
Here are some general rules for potted plants :
• The potting material should never be soggy. Water potted plants sufficiently to prevent them from becoming bone dry.
• In general water once a week, but be aware that small pots (5” or less) need more frequent watering than large pots (6” or more).
• Remember that different potting materials and different size potting materials will dry at different rates.
• Also remember that clay pots will evaporate more water than plastic pots and, everything being equal, will dry faster than plastic pots.
• And remember that clay orchid pots, because of their openings, will dry out faster than regular clay pots.
• Conditions are different from room to room.  If you move your plants, observe them to see if your watering needs adjustment.
• If you place plants in decorative containers (china pot or decorative basket) to enjoy them while they are in bloom, keep in mind this will very probably slow down the evaporation of water and plants will stay wet for a longer time.
• Finally temperatures, light air conditioning and heating will affect how fast the potting material dries out.  Be ready to adjust your watering habits as the season changes, especially from spring to summer and from fall to winter.
No matter how careful you are when watering, some water may and will get in between leaves or new growth. If this water stays there overnight, when temperatures become cooler, it may promote the growth of bacteria and fungi that may kill your orchids or the new growth of your orchids.  To reduce risks of this happening you should adopt sound watering practices.
• Water only on sunny days. If the weather is cool, cloudy or rainy, you’ll be much better off waiting a day or two before watering.
• Water early in the day.  This will allow any water that got in between leaves or new growth to evaporate before nightfall.  In our greenhouses we stop watering at 2 PM in the summer, at 12 noon in the winter and at 1 PM in the spring and fall.
• Water your plants with room temperature or lukewarm water as a difference of 10 degrees or more between the temperature of the water and the room temperature may cause injuries to the plants.
• Water from the top till the water runs freely through the drainage holes or immerse the plant in water up to 1/2” or so below the rim and let it absorb water for 10 minutes or so.
Wipe out any water that splashed on the leaves or in between the leaves.  Using a straw is a convenient way of focusing the flow of air to blow out water from in between leaves.
So far we discussed fertilizers, the proper dosage of fertilizers and proper watering, but giving the proper fertilizer in the proper dosage is only part of the issue. We need to make sure the nutrients are made available for the plants to use.
Nutrient availability to plants is affected by PH levels.  See chart on page 15 of “An introduction to Orchids” published by the South Florida Orchid Society.
As an example, Phosphorous is practically not available to plants in the PH range of  7.0 to 8.5.  Availability of the trace element Manganese is mostly available between a PH level of 4.0 to 5.5.  Boron between a level PH of 4.5 to 6.0.
The above mentioned chart (produced by Michigan State University) shows that most nutrients are available at their optimal level between a PH level of 5.0 to 6.0.
An article in the fall 1997 issue of Greenhouse Grower, although not about orchids, states: “When the PH of the media is too high, micronutrient deficiencies can be a problem. If the PH is too low, micronutrients become more available and can lead to micronutrients toxicity in some crops.”
Even if we started with water with an acceptable PH, the PH will change, up or down, depending on the additives (fertilizer, root solution, ....) we used.  So, after we added all additives, we must adjust our PH to a level that will make these nutrients and other additives available for the plants to use.
Most orchid sources recommend a PH between 5.5 and 6.5 for orchids and that’s what we aim at after adding nutrients and / or other additives ( i.e. Zerotol, Protekt,...).
First of course you have to have a way to measure the PH of the water.  This is done with a PH meter which you immerse into the (well) stirred water containing all your additives. A PH meter costs from about $ 65 to over $ 100.
Two products are available for PH adjustment from Growth Products in White Plains, NY (800-648-7626). PH booster (0-0-25 liquid potassium) raises the PH while Citric Acid Solution reduces the PH.  Go slow ! a few drops in a gallon can make quite a difference !  
The final word about fertilizers is from Rebecca Tyson Northen in her book Home orchid growing :
“After trying several (fertilizers) on your own plants, you yourself may come to have a preference for a certain one.  This is good.  Is shows that all is in rapport between you and your plants.”