Fill hot tub with rainwater?


Nov 29, 2020
Hi, we are new hot tub owners- hot tub came with the house and we are just learning the basics.

Wondering if it is a good or bad idea to use rainwater to fill the tub, assuming we would get a rain barrel and collect rain off the roof of the house (typical shingle roof) and run it through a filter to avoid leaves and dirt. We live in Seattle. I haven't tested the rainwater with a test strip yet, but wondering if there are other chemistry concerns other than what would show up on a typical test strip.

Thank you!

-Jessica & Will
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TFP Guide
Jul 21, 2013
Northern NJ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Welcome to TFP.

Rainwater can be great fill water if it is not contaminated during the runoff from your roof.

Here are searches of prior threads on the topic...



In The Industry
Mar 21, 2020
Cabool, Mo
As I understand it, moisture in the atmosphere does not condense spontaneously but needs a particle to condense on, thereby cleaning the air of particulates. As it falls it picks up more (phosphates, smog, pollen, forest fire smoke, dust/dirt, algae (and other) spores, bacteria, and even pesticides/herbicides (google "it's raining round-up" if you want to be scared). Then it lands on your roof and washes it off, picks up the crud growing/ rotting in the gutters, and finally ends up... in your spa?
I can't say myself, having never tried it, but I'm not about to try it. ;)
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Nov 29, 2020
Interesting points, thanks! Also did the math and realized it's <$10 to fill it from the hose, so that's negligible compared to everything else and doesn't warrant investing in a rain barrel and gutter system.
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