That water doesn't just disappear from the face of the earth. It'll turn back up again.
Yes, there are differences in using water in one place versus another. I kind of think "growing food" is pretty important use for water though. If OP doesn't want the farmers to use the water for agriculture, then what is it being saved to use it for? Watering golf courses?
There is a small lake. This small lake is used as the freshwater drinking supply for a small town. The people in the small town are happy with the water.
Then someone downstream decides to grow some cows. The cows are thirsty and use a lot of water. The water comes from the lake, but there is enough rain so the people are still happy.
Then the rain stops. The lake shrinks, but the same amount of water continues to go to the cows. The water is poured onto the ground at the cows' feet. It is surely not wasted, because the water is going into the ground, but the people in the small town do not have enough water any more. They are less happy.
raldi's not calling for farmers to stop using water. He's calling for them to make the same reductions in use that everyone else has had to make. And, yeah, the water really is no longer available once it's used; Lake Oroville is not exactly the voluminous body of water it once was.
There's not really anything terribly controversial here.
When California growers tap into aquifers to grow their almond-beef-whatever, they're not using a renewable resource. They're using a very finite resource. The aquifers in CA are in real danger of tapping out. Why do we care?
1) it takes a huge amount of infrastructure to move around surface water
2) it takes a huge amount of infrastructure to clean surface water, whether we're just taking out the antibiotic residue and dirt and THC or desalinating
3) the cost of this transportation and purification infrastructure will dramatically impact where people can live and grow their food.
Moreover, aquifer depletion has some funky effects. Sinkholes in Florida that swallow houses come from aquifer depletion -- the ground there is riddled with holes that really need to full of water if you want to support weight [1]. Some lakes start draining if they're (somewhat unusually) geologically linked to a declining aquifer, like White Bear Lake in Minnesota [2]. Part of the culprit in MN is that people can drill wells and use up to 10,000 gallons per day without a permit. Switching to surface water is an option in the Midwest, and the municipalities mentioned in MN are thinking about switching to Mississippi river water. But in central California, what surface water are you going to use?
Last, for the self-interested, aquifer water often makes the best beers :)
[1] http://www.livescience.com/27659-florida-sinkhole.html [2] http://www.minnpost.com/cityscape/2012/11/why-white-bear-lak...
Not to mention the fact that you don't live in one of the few places with abundant fresh water, even during a drought.
But you are correct that they we're asking people to water their lawns once and a while. The difference here is that Ottawa gets its water from the Ottawa river which is a main tributary of the St-Laurent and is itself fed by a massive watershed starting about 7 hours north (funny thing, as you drive up highway 11 you will pass a sign that say "Now entering Arctic watershed").
We're fooled into believing water shortages are environmental problems we need to make sacrafices to prevent. But just paying more for more expensive, higher volume production or recylcing would work too. Eg Isreal.