Issues with using rainwater for everything pool construction and maintenance related


New member
Oct 14, 2016
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...


Mod Squad
LifeTime Supporter
Jul 10, 2012
Tallahassee, FL
I am looking for a thread that talked about the importance of using the proper pH levels water with the plaster. I will keep looking but two eyes looking are better than one so do some searching with me and maybe one of us will find it.


TFP Expert
Platinum Supporter
May 23, 2015
Tucson, AZ
If you do use the rainwater for initial filling, you're going to need to adjust the pH, TA and CH. There's an entire article here on plaster startup options and one thing is critical - the calcite saturation of the initial fill water is critical to proper plaster curing. In a typical bicarb or traditional startup, the alkalinity and CH are both raised to ensure that the water does not leach calcium from the plaster while it is curing. In fact, you want very little emission of calcium from the plaster (ie, plaster "dust") and you are trying to provide enough carbonate alkalinity so that the "carbonation" process of the plaster surface proceeds at a reasonable pace.

For general top-off's of the pool after evaporation, rain water is perfect. You don't typically add a lot of fill water for top-off's and so the pH won't be changed much. However, if the TA and CH are both low, that means you won't be adding those ions as well which helps to maintain proper chemical balance. Raising TA with fill water tends to drive pH up and raising CH over the long term means you increase the calcium scaling potential. I live in a very hard water area and I recently had my autofill replumbed to get it's water from my whole-house softener. Before that, my CH would easily go up 250-300ppm per season. Now my CH decreases as the fill water adds zero calcium. The TA is still high (~100ppm) so there's always an upward pressure on pH from that.

Plaster Startup Options