This distance was originally maintained to prohibit possible storage water contamination from flowing into a public water supply or water well. In this case the gap provides a separation which makes a barrier to contamination of the stored water through direct and prolonged contact with outside debris which may have collected on the roof.
Puwang na ito umiiwas sa kontaminasyon ng mga naka-imbak na tubig sa pamamagitan ng direktang kontak sa materyal na maaaring mangolekta sa bubong.