How do you get a golden watering can in Animal Crossing

Keep your town perfect for fifteen days and ask about environment at city hall to be given your can.
There are many formulas for making a town perfect. I found an easy way. Every day I went around town planting flowers from nook and removing dead flowers and weeds. I planted so there was always at least one flower in view at any point on the ds screen, or if there were no empty spots, I doubled up flowers that they might hybridize, or added more to the houses. For trees I just planted more fruit around town, distributing them evenly but leaving paths where I prefer to run. I never planted flowers on these routes and if a flower grew in my way I moved it.
One day a jacob's ladder grew, it looks like a lily of the valley plant and can be picked and replanted elsewhere. The more perfect your town, the more of these will grow. Keep it going for two weeks and check at city hall periodically. So long as you have this flower blooming, you're on track for the golden can.
For these two weeks you'll need to be able to log in and perform basic maintenance, picking weeds, picking up shells, buying and planting flowers.