The water here signifies the Triune God as the water of life flowing out from eternity to quench the thirst of His people (Gen. 2:10; Exo. 17:6; 1 Cor. 10:4; Psa. 36:8b; Psa. 46:4; Zech. 14:8; John 4:14; 7:37-39; Rev. 22:1, 17). The factors that caused the river to flow forth out of the house were
1) the building up and completion of the house;
2) the living of the people according to the pattern, laws, and statutes of the house (Ezek. 43:10-11);
3) the service of the priests (ch. 44);
4) the offering of all the offerings (chs. 45—46).
The more these factors are present in the church, the more the flow of God will issue forth.