The ruling on tayammum (dry ablution with clean earth) for an elderly person

Question:
Is it permissible for an elderly person to perform tayammum (dry ablution with clean earth) if he is sometimes aware and sometimes affected by things that are not desirable?

Answer:
Tayammum (dry ablution with clean earth) is not permissible except in two cases. The first case is the absence of water; this applies to both the sick and the healthy person who cannot find water. If you do not find water, you perform tayammum (dry ablution with clean earth). The second case is when a person has water but is unable to use it due to illness, or because he needs that water for drinking, cooking, or watering his animals, and if he used it for wudu' (the ablution for prayer), the scarcity of water would cause him hardship. In this case, he performs tayammum (dry ablution with clean earth) and conserves the water for his needs. However, if a person has the ability to use water, the water is present, he is able to use it, and there is plenty of water to cover his needs and his wudu' (the ablution for prayer), then it is obligatory for him to use the water, and his tayammum (dry ablution with clean earth) is invalid.