You have to use whatever the manufacturer mentioned. Sterile water for injection will be available as such. Otherwise, use deionized distilled water or millipore water. PBS/ Saline , unless specifically mentioned , is contra indicated, since it can alter the pH and isotonicity of the final solution. Quantity of water to be used is also important, becoz it can alter the absorption / can cause deterioration of the product. The quality and quantity will be specified by the manufacturer. If you are using pure chemical, get the existing literatures of already done works