What is the meaning of "perfecting ablution despite hardships," and does it include using cold water in winter when warm water is available?

It is Sunnah (definition) to perform ablution thoroughly (isbagh al-wudu') during disliked circumstances (makarih), meaning to complete it despite intense cold or body pain, and the like. It has been reported that the reward increases with hardship. On the authority of Abu Hurairah (may Allah be pleased with him), the Messenger of Allah (peace be upon him) said: "Shall I not tell you of something by which Allah erases sins and raises degrees?" They said: "Yes, O Messenger of Allah." He said: "Performing ablution thoroughly during disliked circumstances, taking many steps to the mosques, and awaiting prayer after prayer; that is the Ribat (guarding the frontiers)."

However, this does not mean intentionally seeking out hardship or demanding it. Hardships are not among the objectives of Sharia (definition). But if an act of worship cannot be performed except by encountering hardship, then the reward is greatly magnified. A person should not make things difficult for themselves. So, if one has something to warm the water, they should not use cold water to gain reward. Rather, the easier the act of worship is, the better.