Ask Mr. Smarty Plants

Physocarpus opulifolius 'Jefam' (Amber Jubilee™ Ninebark) is a cultivar of Physocarpus opulifolius (Ninebark), a North American native plant, but not native to California.   Its native habitat has a higher moisture content (rainfall and soil) than most of California so its roots are trying to find that level of moisture.  This may be one reason its roots are getting into your water pipes.  Native California shrubs would be a better choice since they are accustomed to growing with less water.   Here are some native California shrubs that are better choices for your privacy shrub:

Fremontodendron californicum (California flannelbush)

Arctostaphylos manzanita (Whiteleaf manzanita)  Here is more information about one of the cultivars, Arctostaphylos manzanita 'Dr. Hurd' from Las Pilitas Nursery.

Woodwardia fimbriata (Giant chain fern)  This is not a woody plant and the roots would not expand so much.  It grows in part shade and moist soils.  This would be a good choice if your soils are moist.  Here is more information and photos from  Yerba Buena Nursery in Half Moon Bay, CA.

Heteromeles arbutifolia (Toyon) grows in sun, part shade and shade and in dry soils.

Prunus ilicifolia (Hollyleaf cherry)  grows in sun and dry soil.  Here is more information with photos from Las Pilitas Nursery.

You could consider installing root barriers around your shrubs to keep the roots from growing into your water pipes.  Although the concern for installing root barriers tends to be for preventing roots from harming concrete foundations and other structural components, they can also be used for preventing roots from entering plumbing and other water pipes.  Here is more information about root barriers.