When the right to require the performance of the act is clear and it is apparent that no valid excuse can be given for not performing it, a peremptory mandamus may be allowed in the first instance. In all other cases, the alternative writ must be first issued, except that a peremptory mandamus in the first instance shall not be given in any case involving the delivery of irrigation water if the Director of Natural Resources as defined in section 25-1062.01 is a party.