When adding water to the pool, if the water supply should be accidentally shut

down at the plant and the valve would be opened lower than the pressure level,
the vacuum of the water leaving the line would pull the pool water over into

the water main.

We put a fair gap between the water line and the pool line. There is no possible
chance now of a vacuum being formed. To be doubly safe we cut off the discharge
from the filter into the pool above the water line. There is no possible chance

of contamination into the main’ from the pool.

When running the alum and soda ash into the pool water it is delivered under main
pressure, which is on an average of 40 lbs. greater pressure then the circulating
pump pressure. If in adding this ion the main pressure Wouka drop lower than
the pump pressure there would be a tendency to run this alum = soda ash water

back into the main.

(Suggestion for Dr. Alle only: Suggest take that in on outlet side of filter
and there would be no possible chance of contamination into the main, as the

resistence on the outlet line of the filter is negligible.)