Metropolitan District yesterday ordered and other Boston community restrict their use of water the current drought. MDC told Cambridge to wash their cars; water or gardens; wash down , sidewalks and use ater-cooled air condition- fill swimming pools, or fountains not equipped reciculators. MDC warned that residents the instructions would water turned off. is not actually faced with of water -- the MDC's has enough to supply the two years, even with no problem is that increased for water has taxed the distribution facilities. officials promised that the would not affect Harvard scientific projects that water.