The short answer: it's a very big market.
In the U.S., households often want "even cleaner" water. Look at the bottled water market (which is wasteful but huge), the home purifier market (like Brita), and the residential softener market (like Culligan) where systems cost a few thousand dollars.
The bigger or more addressable market might be in industry: power, mining, agribusiness etc. They have a hard business case for either purifying waste-water or for increasing quality/decreasing cost of available water for crops.
Climate change is tragically accelerating the need for investment in infrastructure related to water.
You'll need to dig more, and start talking with prospective customers/channel partners to get a real strategy in place, but hopefully this helps you along.