Drinking Water

A recent radio programme reviewed UK government advice on various health issues and considered how effective it was.  In particular the programme researched:
-Fruit and vegetables -5-a-day   (smoothies don't count)
-Physical exercise -150 mins per week  (going to the gym once a week  doesn't work)
- Alcohol consumption -3-4 units/day for men and 2-3 units/day for women (no-one understands what a unit is.)
The conclusions seemed to be that the public are so confused by interpretation and ill-informed advice from other sources that the government has been wasting its time. The government has exacerbated the situation itself by changing its advice in an effort at clarification.
Things are no clearer in the area of drinking water. It seems de rigeur to carry a bottle of water everywhere nowadays. When questioning this I am informed that, according to the government, we must all drink 2.5 litres of water a day. This appears to have originated from  a wartime recommendation which did, in fact, make that point but continued to say that most of this we obtain from food. It is this slipshod attitude to accuracy  that leads to confusion with sometimes tragic results.  The current advice from the NHS is that we need 2.5 litres of water per day. Of this one litre is obtained from food and 0.3 litres from 'recovery'. So we need to drink 1.2 litres of water per se.
The Mayo Clinic in USA has different advice for Americans: men need 3litres and women 2.2 litres.  Apparently in the USA only 20% of this is obtained from food. Perhaps the American diet has a lower incidence of fresh fruit and veg from which to obtain fluid?
So how is this advice dangerous?  Apart from the impact on the wallet by buying bottled water when the tap stuff (in the UK at least) is equally good, I looked at the London Marathon for some indication of how people fared in a situation where water consumption might be considered critical.   Over the thirty years from 1981-2011 ten men and one woman died during the race. Causes of death were as follows: 
Heart problems - 7
Underlying health problems - 2
Drinking too much water - 1
Inappropriate drug use - 1
Too little water - 0