(a) Section 15.1(b) of the Delaware River Basin Compact provides that “no provision of section 3.7 of the Compact shall be deemed to authorize the Commission to impose any charge for water withdrawals or diversions from the basin if such withdrawals or diversions could lawfully have been made without charge on the effective date of the Compact; *  *  *” In compliance with this provision: There shall be no charge for water withdrawn or diverted in quantities not exceeding the legal entitlement of the user, determined as of October 27, 1961. Each water user may submit proof satisfactory to the Commission of the factors constituting legal entitlement, as defined in paragraph (b) thereof. In the absence of such proof of these conditions as of October 27, 1961, the quantity of water exempt from charge to each user will be the legal entitlement of the user determined as of March 31, 1971.

(b) For the purposes of paragraph (a) of this section:

(1) Legal entitlement means the quantity or volume of water expressed in million gallons per month determined by the lesser of the following conditions:

(i) A valid and subsisting permit, issued under the authority of one of the signatory parties, if such permit was required as of October 27, 1961, or thereafter;

(ii) Physical capability as required for such taking; or

(iii) The total allocable flow without augmentation by the Commission, using a seven-day, ten-year, low-flow criterion measured at the point of withdrawal or diversion.

(2) Physical capability means the capacity of pumps, water lines and appurtenances installed and operable, determined according to sound engineering principles. The physical capability specifically includes plant facilities actually using water, but excludes facilities which may have been installed in anticipation of future plant expansion not yet realized.

(c) Whenever adequate records of legal entitlement for agricultural irrigation purposes are not available to the Commission, such legal entitlement shall be measured by the maximum number of acres under irrigation by the water user at any time during the year ending March 31, 1971, allowing one acre-foot of surface water annually per acre irrigated.

(d) Notwithstanding the provisions of paragraphs (a), (b) and (c) of this section, there shall be no charge for water made available from storage where:

(1) The cost of the storage facility has or will be otherwise paid for by the user,

(2) Such storage controls a drainage area, and

(3) The use does not exceed the yield of such storage without augmentation from other surface water of the basin.