It is often mentioned that one should not drink distilled water. Why not ? If so, how much distilled water would be harmful, and what would be the health consequences ?

I was watering my plants and some of the water spilled onto a mushroom that was growing in the pot.  The water turned red shortly after making contact with the mushroom.  What caused this?

I was asked by my dad today:

How come if a basin full of water is dyed black, when you take some of the water out with a syringe it comes out clear again?

With my P7 class which was studying the rain forest, we also looked at the differing rainfalls in Brazil and the UK and the water cycle. One of my pupils noted that part of the water cycle information stated that all water on earth is automatically recycled through the Water Cycle so why do we need to worry about saving water. I tried to reassure him that it was to do with the limited amount of fresh water on the planet but would like some "official" confirmation of this.

Following the recent spell of cold weather, I noticed that there are still piles of dirty snow with sand or grit (but not salt) in them, but all the clean snow has melted.

I was walking along a canal several days ago, and, the UK weather being what it is at the moment, the canal was frozen. However under all the bridges that crossed the canal, whether footbridge or road bridge, the water was unfrozen. What is it about the bridges that stops the water under them from freezing?

My girlfriend and I were having an argument the other day. Sometimes when it is cold in the kitchen, I turn in the gas hob to warm the place up. The argument is that she claims that the room gets hotter if you put a pot of water on the hob to boil and let the room get steamy. I disagree and think that the room gets just as hot without boiling a pot of water.

Who is right? Does the room get hotter with the pot of water or does the room get just as hot without it?

The cold snap we're experiencing in Britain at the moment has made me ponder this.  Answers from my friends and relations so far have included:

Because the water is moving (But how does this stop it from freezing?)

Because the water is under pressure

Because the temperature is above zero underground

Beacuse of the otters that the water companies keep swimming around in the pipes (I think this one was a joke)

So...why doesn't the water in the mains pipes freeze when it is below freezing point outside?