For starters...I am not challenging you and not trying to be short with you.
My point here is that if renting equipment were the only answer, there would be more people renting than buying. Apparently, you live in an area with a reasonable demand for your service and a lesser amount of competition. That is great for you...you have clients that are willing to pay the price that you quote for the work they desire to have done. However, if you get into a situation where you are bidding for a job against a guy that has his own equipment, and willing to work for the same amount per hour, that you are...you will not be able to match his bid and make the same amount of money due to having to pay the rental on the equipment. Now, I am not advocating that you buy anything...my point is that if you do this for say, 10yrs, there will be times that you are required to compete against other reputable service providers that own their equipment...you will lose some of that business. The bad part about this is...you probably will not know this until you don't get the jobs...and may not know the reason, even then. It will just be money that you do not make. Also, if some of your competitors learn that you are renting your equipment...they can and will take further advantage of your rental cost, with their bidding. The fact remains...with all other things being equal, the competitive advantage will go to those that own their equipment, more times than not.
The reason that I opted to buy a hot unit up front is the fact that I was approached by 2 business owners that heard that I was starting a pressure washing business...they are wanting to have their businesses cleaned. After their mentioning this to me, I went around to several businesses and just asked them if they MIGHT be interested in having cleaning done and they all replied that they would. Now, I do not have rental equipment available within a reasonable driving distance. I am not willing to drive 120 miles round trip to rent a piece of equipment...that is time and gas that I can spend hunting, fishing or doing something else of more interest to me. I will buy the equipment up front and the difference in cost will be covered in the first year and I will still have the equipment...and if that is not the case...well, I will just have a hot water side of a washer that is not used. There is not a single pressure washer business in my county...other than a couple of lawn guys that do a little...and none of them have hot water. My town is kind of the shopping hub for about 4 counties...so, there are a good many eating establishments here out in the vicinity of all of the shopping area. Also, in this area, I think that the potential for some commercial work is just as good as that of the residential...cause there is no one around that does it and it is very evident...dirty businesses everywhere around here.
I am probably coming at this from a different angle than you...I am seeking to work part time. I would like to consistently do a job or two a week...I think having the hot water will be an advantage to me, in that regard. I think there will be times that residential work will be kind of slow around here and perhaps I can get a little commercial cleaning to fill some of those slow times. It may not work out that way...guess I will see.
I will say up front, getting this business going will be a challenge. It is going to require my knocking on doors and calling on businesses. I imagine that Facebook will be my prime source for online advertising as most folks will be less likely to do search engines to find find pressure washing services. I can look at the amount of dirty property and tell that they have not been doing that up to this point...and I don't really anticipate that changing anytime soon.
At any rate, if what you are doing is working...then there is no reason to change.