Preventing malnutrition and dehydration in older care home residents is complex, with both conditions remaining prevalent, despite numerous guidelines spanning several decades. This policy-mapping scoping review used snowballing search methods to locate publicly-available policies, reports and best practice guidelines relating to hydration and nutrition in UK residential care homes, to describe the existing knowledge base and pinpoint gaps in practice, interpretation and further investigation. Findings were synthesised narratively to identify solutions. Strategies for improvements to nutritional and hydration care include: development of age and population-specific nutrient and fluid intake guidelines; statutory regulation, contractual obligations for commissioners, appropriate menu-planning, implementation and auditing of care, acknowledgment of residents’ eating and drinking experiences, effective screening, monitoring and treatment and staff training. The considerable body of existing knowledge is failing to influence practice, relating to translational issues of implementing knowledge into care at the point of delivery, and this is where future research and actions should focus.