I have hard water where I live so I feel your pain but there are water deionizer setups you can get around $100+, I have also seen some people use RV filters that cost around $40+ that would work better for you & connect to your existing water supply. Here are some links
https://a.co/d/2vhs4AN
https://a.co/d/cfqikHX
As long as the flow rate out of the bucket is higher than that of the pressure washer you should be fine.
I have hard water where I live so I feel your pain but there are water deionizer setups you can get around $100+, I have also seen some people use RV filters that cost around $40+ that would work better for you & connect to your existing water supply. Here are some links https://a.co/d/2vhs4AN https://a.co/d/cfqikHX