Water does not damage silk, but there are cases when you absolutely shouldn't use water on a silk garment.
More Info: Though water does not itself cause damage to silk, the fibers are very delicate and are easily broken when wet.
Follow the Label Care Instructions to the Letter
Some silks are hand washable; others will only survive a professional dry cleaning. Silk is highly absorbent, so the fiber takes well to dyes. There are many dyes, that when used on silk will bleed when they come in contact with water. This is usually why many silk items are dry-clean only.
To err on the side of safety, for those silk garments labeled ‘hand-washable' wash these garments separately from any other laundry. The dyes may still bleed. As water weakens the silk fiber, use a very light hand when hand washing. Never scrub at a stain and do not wring the garment to squeeze out excess water. Instead, lay it flat on an absorbent towel and roll it up to remove excess moisture.
Even if your silk garment is labeled as hand-washable, do not use water to remove a stain. Water will set or even expand certain stains. Adversely, do not wash your hand-washable garment in water if it has a stain. If you spill a liquid on silk blot very gently to absorb it. Rubbing can cause the weak fibers to break and may leave you with a light spot.
Silk Does Not Like. . .
Alcohol: Any alcohol based liquid, such as hair spray, nail polish, and perfume, should never touch silk as these could cause the dyes to run. If possible, primp prior to dressing and ensure that all of your cosmetic products are fully dry before dressing.
Sunlight: Sunlight will yellow white silk and fade dyed silk.
Perspiration: Silk reacts to the chloride salt in perspiration and deodorant and will leave a permanent stain.