I live in Mexico and am married to a Mexican woman. She owns here home and has apartments. She had two apartments and we are now up to seven. Our water comes from the town we live in and we get water 2.5 to 3 hours daily. The water comes from a supplied 3 inch line in the street and comes through a .5 inch tube to an underwater storage. We have a pressure tank to supply water to the house and apts. We have a problem having enough water so we bought a secon line to the storage tank. The original line is about 28 years old. The difference between the two lines is equeal to me taking a leak 28 years ago versus now. The old line has very little flow and pressure compared to the new line. I know the old line is pretty plugged with algae because I had to repair a leak about a year ago and the piece of old pipe I removed had a lot of growth in it. How can I backflush the old line to clean it out and what would I use? A friend told me to use acid to backflush the old line. But what acid and how do I do that? The pipe going into the underground storage tank has a float on it to shut off the water when it Is full. Do not know what type of acid or how to get the acid solution to run back through the pipe.

Maybe using acid in Mexico is OK but without a total disconnect from the supplied water system, you will be in big trouble from the EPA in Estados Unitos.

Sounds like the old .5 inch line's galvanized and is clogged with rust, (see image) Your solution is NOT to contaminate your system with acid but to replace the old line with 3/4" PVC. Good luck, Tom