The annual net income from said system of water works, as defined by said deed from the said Laura H. Jennings or her heirs, administrators, or executors shall be used for the following purposes, viz., If the said Village installs a sewer system within seven years from date the said annual net income and the accumulation thereof not exceeding in the whole the sum of $30,000.00 shall be used by the said Board of Water Commissioners to pay the cost thereof or to pay any bonds which the Village may incur or any indebtedness which the Village may incur (including interest thereon) for the building of a Village sewer system, not exceeding said sum of $30,000.00. This provision shall not include the cost of future extensions of said sewer but only the initial cost thereof said cost, bonds, or indebtedness for said sewer system shall be canceled when paid and shall not be a claim of the Water Department against said Village or any department thereof. After the cost of said sewer system is paid or after said sewer bonds or indebtedness, with interest, are paid, or if said sewer system is not installed within said seven years, said annual net income shall not be used for the ordinary purposes of said Village or for the ordinary purposes for which money is usually required by law to be raised by taxation, but, subject to the foregoing restriction, shall be expended by said Board of Water Commissioners for the improvement and betterment of the inhabitants of the Village of North Bennington in such ways as the said Board of Water Commissioners may judge best.