I've always thought that running water and sewage removal are basic household needs, and should probably be provided, free (i.e. out of general taxation) for all - within reason. I'd install water meters. Water being free up to a certain amount (per capita) and then charged for by usage. Therefore, if you're reasonably careful you pay nothing, but if you own a swimming pool and re-fill it every so often you get hit big time.
As for sewage - why not a flat rate for every toilet in the house, first one free. Live in a big mansion with 5 en-suite bedrooms, you pay more. Those with septic tanks pay to get them emptied, with one free emptying per year. Simple.