what might be some great ways to promote my business?

Twirl a sign board at a busy intersection that advertises your business.

I think the best way to promote your business is by walking door to door and knocking on doors and telling people that you do water testing....

No...You build a website that says what you do and then you advertise it and yourself.

Have you tried ADVERTISING?

Call a local marketing agency or go on Fiverr and find someone who can MARKET your business through both social media and traditional advertising methods.

You won't go anywhere until you care about how you present yourself. From your writing you're either illiterate or just lazy.

Is this all your experience?

I think you need to get some real world experience, if you don't have it.

All you have is theory. 

If I offer you any business advice I expect compensation.

I'm not sure there is a ton of demand for water testing. Are there groups that talk about it? Facebook or reddit?

Its your field, not mine.