Water is an essential ingredient of bread.
It is necessary for the water to have a slight acid tenor. Alkaline waters tend to slow the action of yeast and harden the gluten. Hard water with many salts as calcium carbonate should be avoided.
Use preferably fresh water with a pH a little below 7. If the water is alkaline, it may be corrected with the addition of minimal amounts of white vinegar, lemon or citric acid. If your water is hard and your bread does not turn out good, you can use bottled non-mineralized water instead of the tap one.
If the water is very acidic, a small amount of sodium bicarbonate can be added to reduce its acidity. This with caution: the excess of bicarbonate will turn your water alkaline, which is undesirable.
This I say in a way of general information. If you have no problems making bread with the water you have, don’t worry about the acidity or alkalinity. If you notice that your bread doesn’t turn out well, just take a sample of your water to a laboratory to be analyzed.
Water temperature: There is a widespread tradition of using warm water in the dough. Personally, I only use cold water (and here in Canada tap water is very cold, even in summer). When I worked in a bakery in Toronto, specializing in traditional rustic bread, I used only cold water. I remember once I measured the tap water temperature. It was winter; outside there were piles of snow and freezing temperatures. The water came from the tap at 4°C (39°F). And with that so cold water, I made my bread smoothly.
During the kneading process and the classical long fermentation time, the dough takes the room temperature. This only involves a slight difference in processing time. This difference in time could affect the fast, chemical process of commercial bread; but is of no importance in the slow traditional process of natural breadmaking.
Cold water is generally used in bakeries. A Caribbean baker told me that in his tropical country they have to put ice in the water to cool it down. Warm water hastens fermentation time and gives the baker no time enough to put all the pieces in the oven before the last made up pieces are over-proofed.
Cold water is especially important when the bread is made with natural yeast. It is true that the process becomes much slower, but at the same time prevents the dough from becoming sour.