California Senate Bill No. 655 was passed October 9, 2015 and went into effect January 2016. While this bill says many things we will focus briefly on the obligation of the property owner to maintain the property free of dampness and mold. If any area of the property you rent is 'damp' or 'wet' then you need to make your landlord aware of it. This way they have the opportunity to take the needed action. If you don't notify them in a timely fashion, depending on how wet things are, then the landlord cannot be held liable for the property being wet or mold growing as a result. You would not be able to collect 'damages' from the owner in that case. Of course, you may want to consult legal counsel on this as needed.
Once you inform the owner and no action is forth coming on his/her part then you have the right to take necessary action to correct the problem that poses a threat to you or your families health. A code enforcement officer or health officer can enforce compliance from the owner on the matter of active moisture or leaks. Some renters are able to 'repair' the situation and then send the invoice to the owner and take it off of their rent but you are only allowed to do this twice in a year. And in this context we are talking about situations that pose a risk to the health and welfare of your family and property.
I have performed many inspections for tenants that had large amounts of moisture or dampness in their unit that was not being addressed by the owner properly, if at all. In a case like that talking with the building department of the city you live in and specifically with a code enforcement officer can help get things rolling to force owner compliance on matters like this especially if you are not in a position to pay for it yourself and then take it off the rent. Be sure to look up 'renter's rights in California' pdf which has valuable information on these issues and more specifically on pages 47 to 52.
Contacting the Fair Housing Foundation for the area in which you live can provide valuable information and insight as to how to address such issues with your landlord. Within 1 to 2 days you will have good information you can use to deal with this type of situation and start the ball rolling to getting things corrected.