How can one perform prayers in a sports club while swimming from morning till evening, given the doubt about the purity of the water? And is it permissible to perform ablution (wudu') with wet clothes and simply cover them, or is it obligatory to perform a full ritual bath (ghusl) and change clothes, or should one delay the prayers until returning home?

Prayer is a great pillar [of Islam]; it is not permissible to delay it beyond its prescribed time. It must be performed on time, according to one's ability. Purity from minor and major ritual impurity (hadath (definition)), cleanliness from filth (khabath), and covering the 'awrah are conditions for the validity of prayer. One must perform ablution (wudu') with pure water and wear clean, concealing clothes when able. If pure water is not available, then tayammum (definition) (dry ablution) must be performed. If clean or concealing clothes are not available, then prayer is performed according to the existing condition, and it is not permissible to delay it. Water is originally pure, and its impurity is not ruled upon except with certainty. It is not permissible to swim in impure water if the impurity is confirmed.