If the person to whom any such pipes or works belong do not proceed forthwith, or as soon as conveniently may be after the receipt of such notice, to cause the same to be raised, sunk, or altered, in such manner as the commissioners require, the commissioners may themselves cause such pipes or works to be raised, sunk, or altered as they think fit; provided that such works be not permanently injured thereby, or the water or gas prevented from flowing as freely and conveniently as before.