Installing a pool in the Austin hill country where the only source of water is a large 31K gallon rain water collection tank. Anyone have any experience and/or know of any issues with using rainwater for everything pool related including for mixing with/shooting the gunite, keeping it wet during the curing period, filling the pool, maintaining the water level, etc.? As expected, the rainwater is slightly acidic PH=6.5) with total alkalinity and total hardness both around 50 PPM. Greatly appreciate any advice you can provide...
Using rain water for mixing with cementitious materials is fine.
I don't see significant issues with using to wetting the gunite down prior to plastering.
But I strongly suggest that you do not use it to fill a newly plastered pool. The fill water should have a positive LSI so that no etching occurs while filling.
About 7-8 years ago, I was asked by a GC to bid on a project whereas a college was expanding their dorms and wanted to set up a rainwater collection system on the premises. The purpose was to collect the water from the structures into the tank (I forget the volume) install a filtration system and utilize the water for irrigation purpose.
The GC was not awarded the project so I essentially lost the bid also but the concept to collect the water and filter it was appealing.
Perhaps this is a consideration for your situation. This would allow for complete control over chemical balance and the utilization of the water for makeup purposes or as you mentioned for wetting down structures or general construction use.
A variable speed pump can be used as an energy saver with an oversized filter such as a large sand filter.