Not drinking out of the same water dish.. And I don't know about the toys... But just spending time in the same environment puts your dog at risk. Most worms in dogs are contracted from the soil and through other infected dogs (eggs are shed in the feces)... They are transmitted fairly easily between dogs and, sometimes even, from dogs to people... But your dog can also get them from fleas or by traveling through infested areas. It's not unusual for a dog to contract worms just by simply walking through the park, or lying in the dirt... and because it is unrealistic to try and prevent your dog from playing on the grass or in the dirt (especially if you want to keep a healthy and happy dog), in many areas there's really no way to stop your dog from getting parasites, you can however prevent the proliferation of the parasites by dealing with them as soon as you suspect that there's a problem.
