This is obviously total bullshit, given the amount of water and maintenance required would lead to a staggering cost. But it wouldn't even work. If just a bit of water could stop a wildfire, they wouldn't be an issue. The water would simply evaporate under the intense heat. Another big issue is embers flying over on the wind, landing on top of something flammable (like roofs of most North American style buildings). Once the fire clears the obstacle, it's done for.

Usually with forest management fire breaks are incorporated. A clearing large enough so a fire on one side doesn't easily cross over. These are often combined with access roads for fire trucks. However when a wildfire is large enough, the heat and embers are easily able to cross over. Especially when the wind is involved. Once a fire gets to that scale, it's very hard to fight and some sprinklers in the ground ain't going to do shit.