Beijing plans to crack down on water use in homes and businesses as northern China faces a severe drought that is drying up rivers and destroying crops. The city’s worst water shortage in nearly 20 years has been exacerbated by water pollution and soaring demand from a growing population. Beijing plans to follow the lead of other cities in the region that have implemented strict quota systems, cutting residents’ water supplies in half and imposing stiff fines for violations. Factories in Beijing that waste water or pollute heavily will be ordered to upgrade their technology or shut down. The nation’s wheat crop is expected to drop nearly 8 percent this year, largely because of the drought.