Water is #1. Water is the MOST IMPORTANT ingredient required by a citrus tree.
1). Water is the integral component in every biochemical reaction that is constantly occurring inside your tree.

2). Water is the substance that moves plant nutrients and all other required substances throughout the tree.

3). Water maintains the tree's temperature through transpiration.

4). Water maintains the turgidity of the tree's leaves.

5). Water maintains the turgidity of the tree's fruit.

6). Water maintains the turgidity of the tree's root system.

Millet

Webster Dictionary
1.Turgid(adj)

distended beyond the natural state by some internal agent or expansive force; swelled; swollen; bloated; inflated; tumid; -- especially applied to an enlarged part of the body; as, a turgid limb; turgid fruit

2.Turgid(adj)

swelling in style or language; vainly ostentatious; bombastic; pompous; as, a turgid style of speaking


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Grapefruits and lemons require about 20 percent more water than oranges. Mandarins require about 10 percent less water than oranges. Trees planted in grass should receive 20 percent more water than trees growing with no turf or ground cover. - Millet

Water is indeed critical to life. However, in the tropics citrus production seems to be enhanced by drought stress. The first rain after the dry season brings forth the blooms. It's such a pretty sight!

Citrus trees do not exhibit any visible symptoms of water stress until most of the available soil (and container) moisture has already been depleted. The setting of new fruit can be adversely affected even at soil moisture depletion levels of only 40 to 50 percent, most particularly from before pre-bloom through the month of June (2-3 month period). At 50 percent soil water depletion the remaining water becomes increasingly more difficult for the tree to extract, requiring considerably more and more energy to be expended by the tree on the absorption of water, at the expense of new growth, and the setting of fruit. Therefore, it is important to insure good moisture levels during this specially immportant time for the production of a good harvest, or possibly for any thing to harvest. - Millet

Severe water stress of course is bad, mild stress seems to cause citrus to focus on reproduction instead of vegetative growth. In Fiji, at least. In the book "Biology of Citrus", Spiegel-Roy and Goldschmidt write (p. 131):

"Moderate water stress seems often to favor reproductive development,. . . Water deficit may often substitute for the cold requirement in promoting flowering. It may also shift the balance from excessive vegetative growth towards reproductive growth, and increase cold hardiness."

It is true that MILD water stress does have an effect on lemons, and is used by lemon glowers to regulate the period of fruiting, so that the main crop will occur during the summer months when lemon prices and lemon usage are at their highest. However, that does not invalidate the long known and long understood reduction of tree growth and fruiting caused by water stress on citrus in general. I also have the book " "Biology of Citrus", and agree it is a good book full ofl value to people interested in citrus. I consider the book as one of the best books written on citrus, and certainly recommend it to the members of this forum. - Millet

By the first day of June, (in the northern hemisphere) the potential size of citrus fruit has already been established. This is because the total number of cells in the fruit has already been determined by that time. Fruit size increases thereafter are solely due to the enlargement of the already existing cells. So the proper cultivation of the tree from a month before bloom (January or February) until June is the most important time in the establishment of a good crop. - Millet (Thomas More - Born 1478 killed London July 7, 1535)

In citrus a rest period appears to be essential for flowering. The duration of the rest period determines the amount of flowers produced. The rest period, preferably of 2 months duration, can be induced either by low temperatures in winter (about (l0° C, - 50F) in the subtropics, and in the tropics by a period of water deficit - not water stoppage- (monthly rainfall or irrigation of 50 to 60 mm). The flower bud initiation occurs during this rest period when vegetative growth is at minimum. It is important to note that even for lemons, water deficits have harmful effects for long-term crop production as compared to when dormancy is caused by a cold period. - Millet

Good day. I have a question. What do is the best to use for hard water for watering citrus?

First of all do you know what soluble salts your water contains, and at what level? If your water is high in carbonates, bicarbonates, sodium, chlorine and other soluble salts, they will build up in the root zone with each watering. If nothing is done to re-leave the situation toxic salt levels will be reached, causing a stunting or stoppage of tree growth, reduction of fruit, defoliation of foliage, and finally the tree's death. With irrigation water containing high levels of soluble salts, never let the containers' medium become dry, doing so greatly increases the problem. The good news is that for hobby citrus growers with just a few container trees, the easiest method to remove the salts from the rot zone is by leaching, with clean clear water. Collect and store rain water for this use. With the rain water, flush the trees root system at the rate of 3 X the volume of the container . Do this once a quarter (4 times a year). This will remove all the salts from the container, giving a healthy medium for new growth. Also if your area receives a lot of rain, you can mix it with your hard water to reduce the salts to a levels of 50-PPM or less. - Millet

Very informative thread!

I have a sheet with information about the contents of my tap water, averaged over one year. There's a lot of info in it, but the question is... how much is OK and how much is too much?

The pH value is also an important factor I believe. According to the sheet, my tap water has an average pH value of 8, which I believe is too high. I'm planning to buy a product to lower the pH value of the tap water hoping to increase the health of my plants...

http://gb.eurohydro.com/regul_ph.html

What do you think of this product?

This is one reason, why one should put citrus trees in pots outdoor during no frost days. Because rain is usually much better than water from tap.

That is true. My only problem is that I use a liquid fertiliser that I cannot apply this way...

You can do, what 1000s people do: collect rain water from rooftop in to the barrel and than use it for irrigation.

there is so many way how to do it, from profesional to amateur way.:
http://mojdom.zoznam.sk/gl/3817/131438/Dazd---voda--ktora-setri

http://www.hobys.sk/hobys/eshop/2-1-Nadrze-na-dazdovu-vodu/0/5/42-Zberac-dazdovej-vody-DN75