Sofa should not be exposed to direct sun exposure, let alone rain washed. True, but if you insist on placing leather furniture in the space outside the house, there is a solution.
You need not be too worried about the rain with a synthetic leather couch. Because the synthetic skin has no pores that absorb water. The difference is with the couch wrapped in fabric upholstery. To which made fabrics, relatively more troublesome. Besides anti-UV, water repellent should be (anti-water) as well.
There is such thing as sunbrella fabric. Cain is not exactly waterproof, too, though. But the narrow pores of the fabric, so that fall or spill water on its surface is not readily absorbed. So there's still time to dry the water falling, splashing rain water, for example, before making the sofa so wet.
In addition there is also sunbrella fabric coated with vinyl on the surface, so water is not absorbed. This fabric is applied to a sofa fit in areas that are often exposed to water. For example, in the pool.
But, however, should remain stationed in the area of the sofa in the house. Or, at best, can be placed on the porch or patio. Because, unlike a wooden chair, acrylic, or metal which is light and easily moved when it rains, heavy enough weights couch.