Canal water was not the problem, it was the quality of the water supplying the canal, with human effluent and chemicals from the textile trades being the major culprits. On the Bridgewater, a stop lock was erected at Hulme Locks to stop the Medlock waters, which feed into the canal at Castlefields, from contaminating the rest of the canal, with a tunnel from the Rochdale Canal to the far side of the stop lock providing clean water for the canal westwards from Manchester.
The Bradford Canal was closed circa 1860 because of pollution caused by the poor quality of the feed from Bradford Beck. Bradford suffered a typhoid epidemic which was blamed on the comparatively stagnant waters of the canal. When reopened in the 1870s, water was not taken from Bradford Beck, but was back pumped from the L&LC at Shipley. Bradford Beck is now considered clean enough to supply the canal if it is reopened/rebuilt.
In the 1850s there was concern over the Liverpool terminus of the L&LC, particularly as there was no current to carry away dirty water. Excess water ran to waste down the Stanley Dock branch, about a mile from the terminus basin. There were several manure and nightsoil wharfs here from which effluent ran into the canal. The then canal manager, who lived alongside the canal at the basin, claimed that there was no significant pollution, though he moved his family away a few years later. hat said, there were also numerous coal wharfs around the terminus, and it is thought that the coal dust countered the effluent in much the same way as charcoal put onto a midden reduces the smell.