You can sue your neighbor on a least two counts. First of all, one who causes water to come on you land can be found liable for trespass. While most people think of trespass as a person entering onto your land, it can also be done through a diversion or direction of water or other matter. Since you have informed your neighbor of the damage of water being caused to your common fence and property, continued diversion/direction of water can also be a basis for claiming punitive damages. A second cause of action is that of nuisance. It is similar to trespass and can be brought when one violates your right to quiet enjoyment of your property. The main problem with your case may be that of damages. You will need to show that the neighbor's activity actually caused damage to your property and in what amount you have been injured..
Yes, you can sue, but you will need to be able to document and to quantify your damage. To make your case stronger, I would suggest having an attorney help you write the letter and document your damage in the event you need to go to small claims court.
Frank W. Chen is licensed to practice law in the State of California. The information presented here is general in nature and is not intended, nor should be construed, as legal advice. This posting does not create any attorney-client relationship with the author. For specific advice about your particular situation, consult your own attorney.