Waterbed Sheets Washing Instructions: 100% cotton waterbed sheets are more difficult to maintain than blends. They should be washed in cold water, and line or tumble dried. They do tend to wrinkle, and can be expected to shrink 1-2% the first time they are washed. This shrinkage is taken into account when the sheets are manufactured. For this reason, they may fit loosely before laundering, and provide a snug fit afterwards.. Do not bleach colors. Always wash deep colors separately before using. Be sure you try the sheets on for size prior to washing.