Food and water

"In itself, the provision of food and water (by whatever means) is the ordinary way of sustaining a patient's life and a minimal part of the care we owe to others. Accordingly, there is always a presumption that nutrition and hydration be provided to a patient, unless this would be futile or unduly burdensome (see Catholic Health Australia Code of Ethical Standards 1.13-1.14).

"In particular cases, however, the provision of nutrition and hydration may cease to be obligatory, e.g. if the patient is unable to assimilate the material provided or if the manner of the provision itself causes undue suffering to the patient, or involves an undue burden to others. As the CHA Code notes, in Australia tube feeding is not normally too burdensome to others (5.12)."

Australian Catholic Bishops Conference
Briefing Note on the Obligation to provide Nutrition and Hydration
3 Sep 2004 (excerpt)
(hat tip to Father Rob Johansen)