Let me start by saying I am not licensed to practice law in CA and I am not giving you any legal advise, I am simply suggesting some things that you should look into. First, you should consult with an attorney and find out who is responsible for teh rain water. In NY for example, property owner's are responsible for making sure that the rain water that falls on their property properly drains (doesn't flood their neighbors property). This is not a hard and fast rule and has a lot of caveats. A CA attorney should be able to look into this for you and let you know what your duties and obligations are regarding rain water. If you do have an obligation to contain your own rain water, you will likely need an engineer to determine whether the water draining onto your neighbors property is in fact your rain water. Finally, if you do have an obligation to contain your rain water, and an engineer determines that it is your water that is flooding the neighbor, you need to hire someone to develop and install the proper drainage system. This could be as easy as planting some bushes or trees in certain areas or could be more difficult like changing the grading on your property or building a retaining wall.
First, I would consult with a Civil Engineer and have him or her examine the property and provide a written report as to whether or not your rain water is causing damage to your neighbor's property.
If your property, and the rain water collected on it, then I would ask the Civil Engineer to propose the least expensive means to correct the problem (trees, short retaining wall, drainage system, etc). If you can afford it, I would have it installed.
If you can't afford it, then I would save up for it, and if damage occurs in the interim, I would place the claim with my homeowners insurance (they may or may not cover the claim).
If youa re in the Los Angeles area and need a referral to a civil engineer, please feel free to contact me at my office ( www.yourlegalcorner.com ).
Disclaimer. The information posted above is for general information, does not constitute professional legal advice, and does not create an attorney client relationship.