Boats could only be used on rivers and around the coast. This meant some very roundabout routes had to be used. Rivers were in poor condition. Parts of the river were not deep enough for boats. The picture shows a "flash lock" which was used to hold back water and then release enough for a boat to pass.

Water could often be in short supply during the summer. There was fierce competition to use it from the owners of water mills. The millers wanted to divert water from rivers for milling grain and would often make it difficult for boats to travel. In the winter, floods could make navigation impossible.

Rivers often had no properly built towing path. Sailing boats were sometimes used, especially on larger rivers, but the twisting and turning and unreliable wind meant this was a poor solution. Teams of men or horses were needed to pull boats and to carry goods between the river and the place where they were needed.

On water, a much larger load could be pulled by one horse. A packhorse on the roads could carry about 180 kg. A horse pulling a cart could carry a maximum of 2 tonnes. A canal or river boat could carry 50 tonnes and still be pulled by just one horse. This was a tremendous advantage of water transport, especially for heavy goods like coal or stone.

Rivers naturally always link to the coast. Much larger coastal sailing ships and barges could carry even bigger loads on the sea. At sea, wind power was much more efficient than the inland horse. By using a combination of rivers and coastal shipping, a heavy load could travel a long distance.

Carriage by water cost a lot less than on land. One horse could carry up to 50 times as much cargo on water as on land and fewer men were needed. It was so much cheaper to carry goods on water that sometimes "long way round" water routes were used instead of short road routes.