pH correction methods

Dear members, we are getting drinking water from a private well since 2006. Since 3 months the water started appearing little rusty. We did the analysis and found out that there is corrosion in pipeline as the Ph level of water is 5 which is low. We can not change the piping since its not very old and its expensive to replace the whole pipe line. Please tell us how to increase the ph level of water before it enters to the pipe line?