If your property currently includes water and sewer in the rent or uses a flat-fee billing, one of the best conservations measures available is to implement either a RUBS or submeter billing program. Studies and experience has shown that residents will conserve water when presented with an individual bill. You can expect savings of 15-30% off your regular property bills, which is hard to match with other methods. In most states, you can even pass through the billing fee, so the program is a no or low cost proposition to the owner.
Submetering was initially rolled out in the western states as a proven conservation measure. Water rates were increasing faster than rents, so measures had to be taken to lower the cost and risk to owners. Since residents actually have control over their own water use, it makes sense to transfer the cost and risk to them. If owners also provide residents with low-flow fixtures to help them better manage their usage, they will be more receptive to the idea. Water and sewer rates are rising on average 5-8% per year, so this issue is not going away. The sooner you involve the residents in the solution, the better off every one will be.