Hmm... Are these wizards recognizably evil?
Or could they, say, sell a couple of these trinkets around.
You know, have it so they can only be activated at a certain time of the day, but create water an unlimited number of times in that time frame (a very well planned spell trap.)
Then, get neighborhoods to buy one or two, to serve the neighborhood. Then, see if you can get the people in charge to allow you to build magical fountains...
Hell, you could sell more than one of those trinkets; maybe a "magical" juice making device (throw Prestidigitation on there as well), that activates at the same time as the device.
Because, if we assume that your town of 10,000 people consists of families of 3.5 people (to allow for children and such), and that you sell a "liquid maker", with outlets for both water and "juice" (two Create Water cantrip traps), as a single unit, you could sell 2,857 units; if you set it so that activating it one way activates it at CL 1, and the actual "event" is CL 20...
That's 228,560 gallons in a round; going for 1,500 rounds would net you 342,840,000 gallons, which is, sadly, less than 1% of the water you need.
At CL 20, you would literally need 3,505,640 devices for every man, woman, and child in the place; 2337 (about) if they continuously create water over 2-1/2 hours.
Now, if we go into metamagic shenanananananigans, we can make those Create Waters Twinned and Repeating to end up only needing 585 devices for each. Person. In. The. Town.
5,850,000 such devices is going to be a little pricey... also, where would you put them?
Now, is the 2-1/2 hours thing truly necessary? Because it would be far more tenable then, due to the smaller number of devices necessary.
To put this into perspective, an individual spell trap of a CL 20 Create Water is (to read the SRD, it would be free, but this is stupid. Therefore, we will take the standard "cantrips are 1/2 spell level for the purpose of crafting") 5000 gp. To have enough, it would cost you 116,850,000,000 gp.
That is the WPL of 153,750 20th level characters; you can bring this down to a mere 5870 20th level characters by using EVERY COST REDUCER IN THE BOOK.
Seriously, I know that there are easy ways to break WBL, but the Imperial Oracles will notice anyone making/moving around that much wealth.
To emphasize, I probably undercalculated that, due to not having a full understanding of trap pricing.
Tl;Dr: It isn't feasible to do. At all. And by not feasible, I mean that you need billions of gp and a bit over twenty-three million such trinkets to pull it off.
However, this is just if you are trying to do this as a player; if you are a DM, the players won't be doing this math.