Water is a commodity furnished by either the municipality or some private agency. If charged at a flat rate according to "frontage" and equipment in the building, there is usually no apportionment of the charge. If however, as is becoming the case of late years, a meter is installed, and a charge made on actual water used, then it is customary to make an apportionment. Readings are taken and bills rendered usually quarterly. It is a simple matter to compute the probable amount of water used since the last reading, and the charge for this should be allowed by seller to purchaser. For great accuracy the contract may, as in the form given, require the seller to furnish a reading made within thirty days of the closing date.