A mud pump represents a huge improvement in drilling over just using two hoses. It improves water flow. A typical mud pump will put out 100 gallons per minute whereas two hoses are only good for about 12 to 15 gallons per minute.
It saves water. Just as important, a mud pump allows you to employ a re-circulating system so you can use bentonite or other gelling material that will solidify the sandy, crumbly walls of your borehole long enough you can drill without worrying about your hole collapsing on your drillpipe