A long winded answer also giving solutions .
BUT YOU ARE WRONG ONLY THE COASTAL RAINS COME FROM THE SEAS ,THE REST COMES FROM PRECIPITATION FROM THE FORESTS.(they can measure the salt content in the rain water and the further inland we go the less clouds are from ocean evaporation)
IT IS THE TREES THAT KEEP THE RIVERS FLOWING
Farmers pump to much from the rivers for irrigation,More and everywhere.more people use water and also contaminate it
In many places people die of the lack of uncontaminated water or even any water and will end u killing for it if they don`t already..
Now with the melting ICE we are loosing 75% of all sweet water supplies on the planet.
25% of the planets surface is land
75%of the surface is SALT water ,and it is rising
97%of the Earths water is salt
fresh water is only 3% of all the Earths water
most of it is beyond out reach
now much ice is melting and running into the seas fresh water lost for ever.
STORAGE or Location of % of the fresh water
ice and glaziers 74%
groundwater 800 meters + 13.5 %
groundwater less than 800meters 11.o%
Atmospheric in circulation 0.0035%
frozen land or permafrost is not included and represent an unavailable storage of 40%
so of the 3% about 11.6 ,is easily available to us ,in rivers, lakes and ground water surface aquifers,more and more of this is becoming contaminated
overpopulation of an extra 70 million people a year (increasing all the time )and expanding agriculture ,which uses 70% of available potable water supplies ,has brought the good(sweet) water supplies to critical levels ,some countries have been in trouble already quite a while .
Now climate change and desertification, because of irresponsible agriculture ,overgrazing and deforestation is damaging world fresh water production .
It is a good reason for concern and if we do not rectify matters by changing agricultural methods ,
reforest ,stop deforestation,
become more economic with water use ,
stop producing more people ,
stop wasting and contaminating water,
we will be in serious trouble all round
and could end up looking like Mars.
I am sure this will fall on deaf ears but these are some of the things we can do
to conserve water use
EFFICIENT WATER USE
IN THE HOUSE
one can connect the sink straight to the toilet cistern and so use the water twice ,first to have a shave and then to flush the toilet
also if you bend the ball valve you can regulate the level of the cistern
Always have your Grey water and Black water separate,so that the sink and shower water goes directly into the garden saving on irrigation and at the same time ,making the sewage smaller and easier to deal with ,
This also goes and irrigates the garden but via a cistern of two compartments and a French drain ,on which you plant trees,
HAVE DRUMS OR A POND COLLECT WATER FROM THE ROOF OF THE HOUSE
And cars can be washed with rain water ,it does not have to be drinking water.
ON THE LAND
Only use small tractors for initial shaping and earth works
then preferably no till methods
Or use deep chisel plows sparingly to minimize disturbing the
top soil further so that organic structures remain intact and continue working ,building soil.
Do not use heavy machinery which compacts the soil and will raise salt content to the surface do not have too many Cows
which will do the same
Compacted soil does not absorb much water.
Economic systems of irrigation, like drip irrigation
and water harvesting design, using a lot of stone walls ,that condense water in the night
and planting leafy plants ,for the same purpose,
Building wind breaks ,to counter act the drying effects of the wind and farm towards Aggro forestal ,using as many trees as possible to limit evaporation .
Using shade nets before we have tree cover
and use MULCH
By cutting down the weeds before they produce seeds and leave them where they fall.
They will cover the ground add even more organic matter on top,(you can use saw dust,leaves green or dry),
Plant big leafed plant around the plots to use for mulch
Conserve soil by using compost,,Utilize all manure from the farm,
Plant DIVERSE,in guilds and companion planting to spread the chemical requirements and releases to preserve soil balance,
Have some tall scattered shading trees at intervals to break the suns rays.
And when you plant make a little space and plant in the mulch.this is the easiest quickest and by far most beneficial way(for the quality of you soil)to prepare the land for planting.
To prevent weeds from coming all you have to do it turn out the lights,you can even use cardboard or black plastic(this is good for strawberries because they will rot if they touch humid ground,and the bugs can get to them).
The humidity is preserved underneath and promotes the development of worms(there exists no better compost than their excrements)and a variety of micro biotic life which together within the mulch produce more topsoil.
The mulch also keeps the ground temperature even and guards against the impact of the rain ,which would other wise brings salt to the surface if on unprotected land.
Mulch also prevents the soil from drying out because of the sun and,wind erosion.
We should not only conserve Water ,we should also collect it when it rains ,make your lawn and garden receptive to absorb water ,like a giant sponge.
As far as catching rain is concerned ,we do this all the time ,and have done so already since Babylonian times,and is a part of the more advanced Agriculture,that existed with the Egyptians,,Moors, Arabs and probably many more
Central ,and South American indigenous people had this idea coupled to their pyramids ,catching the water of the slopes and leading it into tanks or onto the fields .
And many others ,today we call this WATER HARVESTING.
Only Modern Man is totally extravagant with the rain water given ,and complains of the wetness ,letting it run off into the rivers lost forever ,With out even attempting to hold on to it .
And then later complains of not having water ,when times are dryer
So initial energy on Extensive earth works to shape the land to be receptive to water absorption,is to be recommended.
Make terraces when farming on slopes
use living and any other type of barriers on steep slopes to collect and contain any organic material that is about and mobile
In Permaculture the rule is to harvest water to the point of Zero runoff.
This means that all of the rain that falls on an area is absorbed by the terrain and not a drop leaves it.
By building dams,ponds or Swales, with inter connecting ditches,
Bio swales to absorb water
If there are enough of these ;the places ,where before ,the rain water ran over the ground into the rivers and on to the sea ,in a matter of hours or days.
It now runs into absorbent dams or Swales and saturates the ground and eventually reaches subterranean water deposits ,taking many months to do so.
Or it fills up ponds that can be used for Aquaculture.
And so a convex situation that repels water is transformed in a concave ,absorbent one and turning the area in to a sponge.
The more holes the better and if they do not hold the water but leak ,the water is not lost it is in the ground for months
In Spain and Portugal ,which still display many examples of the conquering Moorish influence one can find many remnants of Water harvesting,such as Aqueducts and tanks underneath the patios ,which collect the rain water from the roofs ,to be used in dryer times.
In Arabia ,on a large scale ,land has been shaped to catch and lead,rain water into sandy areas or to agricultural lands.sand is almost as good as dams because it absorbs water and holds it.
Here in Mexico we collect the rainwater in our school for sustainable agriculture,but it is too near Acapulco to trust the rain water for drinking ,and this holds true for most places ,so we use it for irrigation.The rain water from a gutter runs via a filter into a tank.
In Europe in my parents house ,when i was young ,we had a rain barrel,where the water from the gutter ended up .
this was usual in those days ,but i have seen few in modern times.
We can use this concept also in other ways ,
for example the roof water from the rain,via a ditch can run trough the chicken house ,cleaning it and end up fertilizing the vegetable plot
(this is called the creation of energy flow).
This water used to be Ok in times gone by before Air pollution ,
Today i would recommend it only for washing and irrigation
For more information on Water Harvesting
read The Permaculture designers manual by Bill Mollison,which cost about 40 dollars.
and is the best all round book you can get,on Environmental design,.(tagiari publishing, firstname.lastname@example.org)