Islam encourages cleanliness. To ensure this is preformed, it is mandatory that your body and clothing be clean before performing your salaat. Your prayer will not be valid unless your body and clothing are clean. Clothing must be considered tahir and removed of all impurities. Impurities include blood, urine, and excrement.
The following water only, is permissible for Wudu. Natural water such as rain, lakes, rivers (any moving water) and tap water. Only in the following situation are you permitted to perform prayer while your body or clothing is najis (dirty). If you are injured and the body becomes dirty and it is difficult to wash the clothing or body. If you do not know that your body or clothing is najis (dirty), and after the Salaat you realizes it. If you have made wudu and should come in contact with blood that is less then the size of the tip of your thumb. Someone is helpless and must pray with a najis body or clothing; for example, one does not have water to clean the clothing or body.
The purifying of your body is called wudu. The passing of excrement, gas, urine, vomiting, bleeding, touching of sexual organs without clothing, falling into a deep sleep, and laughing loudly during salaat can all break your wudu. Once wudu is preformed and not broken you may perform multiple prayers. Here are some instructions to follow for performing wudu.
To perform Wudu you should first make the intention (Niyyat) to perform Wudu. Call upon Allah at the start of Wudu by saying Bismillah.
Major Impurities and the Purification Method
To remove major impurities from your body, you are required to perform Ghusl, or a full shower. The following acts require Ghusl. The emission of fluids from male or female sexual organs, menstruations, sexual intercourse, masturbation, child birth.
To perform Ghusl you should combine the procedures of Wudu to maximize the level of purity.
Tayammum and the Purification Method
Islam is formatted to adapt to many circumstances that may occur. One such circumstance is not having water available to perform purification. If no water, water that is contaminated, or if water is very scarce you are allowed to perform a dry purification called Tayammum.