I budget the same amount every month, ( or each pay check ).

Means that it is not a lumpy expenditure any more, just part of my True Expenses Rule#2

It may come down to personal preference or how flexible you can be with your budget - I prefer to allocate the cost of my water bill whichever pay week is closest to the due date because this is normally $15 or so. With other (larger) expenses that recur the same way, I'll budget over multiple paychecks.

Hey  Gray Disk , both  negrcian &  pureneon bring up solid suggestions and as you can see already it's really a preference thing. 

I think the point that pureneon brings up is great, because you'll benefit from one method versus the other depending on how large your Age of Money is - aka how much wiggle room you have to budget!

We think the best way is to apply Rule Two: Embrace Your True Expenses . Which would mean that you split up the bill over two months and budget half each month. 

Now, you could take that even further and estimate your water bill over the course of the year - this is what I do. Of course there will be fluctuations here and there, but overall, if you've been living at the same place for a while, you know the peaks and valleys of your water bill.  

1. Take the total amount you spend on water in a year and divide by 12. Let's say that's $500 total, divided by 12 is $41.66. 
2. Then consider if $83.32 (two months of budgeting for water) is enough to cover your highest bill. If it is, then you're all set. Begin budgeting $41.66 each month and you'll most likely have enough money to pay your water bills. Small fluctuations in the cost of water can be adjusted on the go and it won't break your budget!
3. If your highest water bill is larger than $83.32, which it probably is (because that's how averages work, right?), then either increase that monthly budget goal to account for the difference (so maybe budget $50 instead of $41.66 each month) or make a note in that category to budget more beginning at a certain month. Obviously, budgeting a little more each month gives you a peace of mind and minimal maintenance, but many of our budgets can't handle the extra buffer in a category. 

Anyway, I hope that sparked some good ideas! Let us know if you have any further questions on this whole thing!