How much horse power is needed?

When James Watt promoted his steam engine on the market he needed to show its advantages over the traditional power supply by visual demonstration. He counted what average weight an ordinary horse can raise per minute activating a water pump. This measurement unit was named horse power. Thus the power of steam engines shown in horse power meant the number of times a machine can be more effective than a horse. By the way according to the scientists for a short period of time a horse can work with the maximum load which equals to 15 horse powers.