The general consensus is to ...
Published by Peter Styles, Independent - Consultant (retired)
The general consensus is to use plastics for their available range of diameters. MDPE has been used extensively in the UK but most countries prefer HDPE. Be very careful with uPVC as the lower classes can break due to negative pressures under surge conditions. Ductile iron is a great material fro larger diameters. I, personally, would never recommend steel as it pinholes when it fails and it is difficult to find the leaks.