What is the ruling on contaminated water spray scattering onto inner garments when relieving oneself in the bathroom, and must they be washed, or is it sufficient to wash only what was felt?

The fundamental principle is that ritual purity (tahara) remains, and this certainty is not removed by doubt. If you doubt that impurity (najasa) has touched your clothes, then build upon the original principle that it has not. If you are certain that impurity has touched your clothes or body, then it is obligatory to wash only the affected area. Islamic law is built upon ease and keeps a person away from groundless whisperings (waswas). The fundamental principle concerning clothes and the body is purity, unless the arrival of impurity is certain, based on the saying of the Prophet, peace and blessings be upon him: "He should not leave until he hears a sound or perceives a smell."